CONS 340 Lecture

spheroid

A spheroid is an ellipsoid that approximates the shape of a sphere Fun facts: Earth can be approximated by an oblate ellipsoid, but its major and minor axes do not vary greatly In fact, its shape is so close to a sphere that it is often called a spheroid rather than an ellipsoid! ESRI calls Earth a spheroid, but the two can be used interchangeably For most spheroids, the difference between the semi-major axis and the semi-minor axis is less than 0.34%

Displaying Data

-Graphs -Charts -Tables -Maps

Degrees Minutes Seconds (DMS)

Degrees of latitude and longitude are further broken down into Minutes and Seconds

Candidate Key

-Provide tuple-level addressing system -May be more than one per relation

Analyzing Data

-Proximity (which parcels are within 50 feet of the road) -Overlay -Intersection -Zonal Statistics

Attributes

-a property that serves to describe an entity set -all entities of a given set have certain properties in common

Query Language

A computer languageused in database management systems to retrieve, add, modify, or delete data

Selection Type

Multiple methods availableNew selection Add to Remove from Select subset Switch selection Clear selection

semantics relationship

associations that there exist between the meanings of words

There are three main components to geographic data

attributes (what) geometry (where) behaviour (rules, e.g. all streets connected to another street) all 3 together creates a data layer

however, you can:

divide population by area (both ratio scales) and get population density subtract elevation at point A from elevation at point B and get difference of elevation

Great circle arc

- formed by the intersection of the earth with a plane passing through any two surface points and the center of the earth -not a line of constant directions, the shortest route but not the easiest one to travel on

Cardinality Four possible cases exist

-1-to-1 -1-to Many -Many-to-Many -Many-to-1

DBMS

-A Database Management System(DBMS) is a Database(s) (collection of Files), and the associated; programs that operate on the files as well as an organizational structure supporting the files and their use -It is a software system that manages a database Typically provides these functions:Backup/recovery Transaction management Retrieval Manipulation Data definition

Relational Database Definition

-A collection of data items -organized as a set of formally-described tables -from which data can be accessed or reassembled in many different ways without having to reorganize the database tables. -Almost all current GIS are based on a relational database structure.

What is the best ellipsoid for you?

-A datum is a reference ellipsoid for locating points on Earth's surface, how the mathematical concept is attached to the earth itself -Defines origin and orientation of latitude/longitude lines -Defined by ellipsoid and ellipsoid's position relative to Earth's center

Problems

each method is approximate, capturing only part of the real variation a point sample misses variation between points transects miss variation not on transects zones pretend that variation is sudden at boundaries, and that there is no variation within zones contours miss variation not located on contours

Relations (definition)

-A finite set of tuples associated with a relational schema in a relational database -a table is a relation if it meets these six propertieseach attribute has a unique name the order of the columns is irrelevant each attribute entry is single valued; no repeating groups entries in any one column are of the same kind order of rows is irrelevant each row is unique -any table that conforms to these properties is a relation

A Relation in the Language of E-R Modeling

entity set, instances (rows) attribute (column)

Map Projection

-Curved surface (3D) -2D Flat Surface -Approaches to transfer the spherical earth on a two dimensional surface -Some distortions will always occur -Visualize a light shining through the Earth onto a surface

Decimal Degrees (DD)

-Decimal degrees are similar to degrees/minutes/seconds (DMS) except that minutes and seconds are expressed as decimal values. -Decimal degrees make digital storage of coordinates easier and computations faster.

Join versus Relate

-Follow these general guidelines when choosing between joins and relates on your data -You'll want to jointwo tables when the data in the tables has a one-to-one or a many-to-one relationship. -You'll want to relate two tables when the data in the tables has a one-to-many or many-to-many relationship.

how are different spheroid different

flattering factor, how they linked to earth to center (earth-centered datum coordinate system) to some point on earth (local datum coordinate system)

How do you logically connect a 1 to many relationship?

foreign key base on Cardinality

GIS data

modification of reality not reality itself what vs where

thus you cannot:

multiply soil type 2 by soil type 3 and get soil type 6 divide urban area by the rank of a city to get a meaningful number subtract suitability class 1 from suitability class 4 to get 3 of anything

Database

not easy to interperate

Why was the "student_courses" relationship modeled as a relation?

not very effective, if not relation, too many column of student/ courses in the other one, the number of students in a courses, and the number of courses a student is taking would change over time, and if a courses have 500 students, many column would be null

The Mixed Pixel Problem

one dominates winner takes all edges separate

A Relation in the Language of RDBMS

relations (tables) ,tuples (rows), attributes (column)

What is Geodesy?

-Geodesy is the science that studies and determines the shape and dimensions of the Earth. -Different models have been defined to represent the Earth's shape, varying in their complexity and in the accuracy that they represent the size and shape of the Earth.

Object Based Models

-Georeferenced means they are linked to a coordinate system -Basic Data Unit = Object (point, line, poly) and is implicit (feature class, shapefile, vector based model) -Spatial information must be explicitly encoded

Learning Objectives 07

-Get your mind around relationships -Perform the second part of an Entity-Relationship (E-R) Modeling exercise -Choose the proper cardinality for a relationship -Create full blown E-R Diagrams -Apply the concepts of primary and foreign keys

Images- stored as raster stack

-Images can be either simple (one layer) or composite (a collection with multiple layers). Simple-a black and white image -Composite-multi-spectral satellite images where each layer stores the amount of reflectance from a different wavelength of the electromagnetic spectrum. -By assigning different colors to each layer, analysts can evaluate factors such as land cover type and vegetation density.

From Conceptual to Logical

-In E-R modeling we do not know how we would actually hook up entity sets -But once we have a conceptual model we need to figure this out -Therefore we move into what is refered to as Logical Modeling

Raster Structure

-In a raster GIS, data are stored in a grid of columns and rows. -The intersection of each row and column is known as a cell. -Each cell corresponds to x and ycoordinates in the real world and contains a z value that can represent anything from elevation to census data.

Table

table=entity set=entity type=relation

Reliability of Measurements

the consistency with which a change in the property produces a change in the value of the variable -More is better, but cost/benefit has to be considered

Storing Data

vector (x, y coordinate) rastor e.g. represent and road and store it

Transferring and exchanging data

-May create errors. -Especially between different formats such as vector and raster. -Vector to raster is easier than raster to vector.

Geoid

-Physical approximation of the figure of the Earth. -Shape of the surface of calmed oceans, in the absence of other influences such as winds and tides. -Computed using complex physical models and gravity readings of Earth's surface. -Used to measure surface elevations with a high degree of accuracy.

Vector Strengths

-Point-line-polygon format is familiar -Vector systems have small storage requirements -As objects, individual features can be retrieved individually for processing -A variety of descriptive data can be associated with a single feature (raster can only record 1 thing, vector can record one in 1 data type, in a single file format) -Superior cartographic products

Points

-Points use a single coordinate pair -Show the location of an entity which is assumed to have no dimension -Examples include: gas well, light pole, -Attribute data is associated with each point such as height of pole, power source and so on...

Cylindrical Projection

-Projecting a spherical surface onto a cylinder Longitudes equally spaced Latitudes unequally spaced Scale is true along the equator Shape and scale distortions increase near poles Best for equatorial or low latitudes

Vectorization

-Raster to vector conversion -Continuous versus discrete rasters -Where to draw the lines becomes an issueTolerance -Lines typically are smoothed

Apply this with a RDBMS in RQBE

-Relational Query by Example -A simpler method of creating queries -Generates SQL behind the scenes -Facilitated by specific software interfaces

Relationships

-Relationships conceptually link two entity sets -Relationships describe the association between these entity sets"is a kind of" "owns" "works for" "offers" -These are known as semantic relationships

Join

-Returns a relation consisting of all possible tuples that are a combination of two tuples, one from each of two specified relations, such that the two tuples contributing to any given combination have a common value for the common attribute(s)of the two relations (and that common value appears just once, not twice, in the resulting tuple).

Project

-Returns a relation consisting of all tuples that remain as (sub)tuples in a specified relation after specified attributes have been eliminated. -Students [Name, Major] -Returns a relation of the Name and Major attributes of the Students relation column

Rhumb line

-Rhumb line, loxodrome or constant azimuth -line which makes a fixed angle with all meridians; spirals to pole

Querying Data

-SELECT CntryName, PopCntry -FROM Countries -WHERE Landlocked=No -ORDER BY CntryName

Basic SQL Statements

-SELECT column_listFROM table_list{WHERE where_clause} {ORDER BY column_list} {GROUP BY column_list}Retreivedata from one or more tables in the database -INSERT source INTO target(columns) VALUES (value_list)Insert a tuple(row) into a table in the database -UPDATE target SET col_val_pair_list{WHERE where_clause}Modify data of one or more tuplesin a table -DELETE FROM table {WHERE where_clause}Delete a tuplefrom a table

Continuous ("variable")

-Whatever the precision of the measurement scale there is in principle an infinite number of levels of the property between any two measures (values of the variable) -e.g., length is continuous

A GIS answers spatial questions

-Where should I buy a home? -What is the population of Vancouver? -Where can the forest be harvested? -Where should land be protected? -What is the impact of climate change on area burned in Canada? -How many black bear can be hunted this year in Alberta?

Foreign Keys

-a primary key occurring in another relation is a foreign keyin the second relation -a foreign key is the controlled duplication of an attribute in one or more relations -these keys help define the relationships between relations -it indicates directionality in that the foreign key comes to one relation from another (foreign) onethis is a parent/child association a foreign key on a child relation is a primary key on a parent -foreign keys do not assure uniqueness; they define associations between relations -A foreign key may be null, and almost always is not unique.

Continuous World in a GIS

we can represent such variation in several ways: by taking measurements at sample points, e.g. weather stations by taking transects by dividing the area into patches or zones, and assuming the variable is constant within each zone, e.g. soil mapping by drawing contours, e.g. topographic mapping -each of these methods creates discrete objects the objects in each case are points, lines or areas

Entity-Relationship Model

-an extended or semantic data model -a type of data model (representing phenomena with data) -comprised of ...entity sets -attributes -relationships

Polygone

-area objects -formed by a set of connected lines -polygons have an interior region -polygons can also share boundaries -attribute data can include area, perimeter, as well as other data link country name etc. -attribute data linked by an object ID

Conic projections

-result from projecting a spherical surface onto a cone -Best for mid-latitudes with an East-West orientation like Canada conical projection surface, secant conic projection

SQL: Structured Query Language

-standard language used with relational databases to build complex logical expressionsto access data -Developed by IBM in the 1970s, has become an industry standard -Considered to be a "4GL"

DataBase atomic components

A DataBaseis a collection of Tables. -A TABLEis a collection of records. -A RECORDis a set of items, usually organized in a well-defined structure. -An ITEMis a description of an object, an event, or some aspect of such a condition (usually in the real world). -Items, Records, and Tables are usually linked according to some well defined structure. -Usually, the definition of these relationships is incorporated into a RelationalSchema

Representing Reality in a GIS

A GIS database consists of digital representations of discrete objects -Our mental models influence how we conceptualize, measure and store these objects -GIS typically forces us to organize the world into like groups of objects (Forest Cover polygons, parcels, buildings, cities, etc.) -Objects are defined by the attributes we choose (name, population, %vacancy, etc.) -Attribute data are measures of REAL WORLD properties (is the number assigned in the database the REAL value?) -How the data got there is of the utmost importance!

What is a database?

A collection of data organized according to a conceptual schema (a structured framework)

Raster Resolution

Advantages:Easy to conceptualize. Overlay operations are easy. Is a two-dimensional array The problem of resolution. For a small grid:Coarse resolution but small storage space. For a large grid:Fine resolution but large storage space. (Slow to process)\

Many to Many

Converted to two 1 to many relationships

Accuracy

Correctness of measure: difference between predicted, measured, or observed value and true value; freedom from error.

Hardware & Software

Currently there are many software providers that produce GIS software but for the duration of this course we will be using Environmental Systems Research Institute(ESRI) software

secant cylindrical projection

Cylinder touches sphere along two lines -both small circles

Developable Surfaces

Cylindrical projections Conic projections Planar projections

Calculating Earth's Circumference

Eratosthenes accurately calculated the circumference of Earth by noticing how the Sun shone directly down a well in Syene(modern Egypt) at noon on the Solstice. He later made a second observation at Alexandria with a pole and noticed a shadow. He measured the angle of the shadow and inferred the circumference of Earth, which was already known to be spherical.

The Birth of Geography

Eratosthenes was a Greek mathematician who lived from 276-194 BC and established the field of geography He was responsible for.... -The first accurate measure of Earth's circumference -Calculating the tilt of Earth's axis -Calculating the distance of Earth to the Sun -Invention of the leap day The first world map of the (spherical) Earth

Conversion from DMS to DD:

Example coordinate is 37°36' 30" (DMS) -Divide each value by the number of minutes or seconds in a degree:36 minutes = .60 degrees (36/60) 30 seconds = .00833 degrees (30/3600) -Add up the degrees to get the answer: -37°+ .60°+ .00833°= 37.60833 DD

Relational Database Management Systems (RDBMS) Learning objective

Explain the function of a RDBMS -Define some basic terms related to relational database -Understand Entity-Relationship (E-R) Modeling -Explain data types -Construct relevant domains -Write entity sets in standard form

Validity:

Extent to which measurements reflect what we intend them to. Measurements can be reliable without being valid; but not valid without being reliable.

Precision

The closeness of measurements to each other.

Column

Field=attribute=attribute

Single User

File geodatabaseA folder of files that is cross platform Datasets can be up to 1 TB in size (with configuration larger) Best default choice -Personal geodatabaseStores data in Microsoft Access Limited to ~250 -500 MB for the entire geodatabase Only supported on Windows

Computer Languages

First generation --machine language Byte level -01100101 Second generation --assembly language A close approximation of machine language -ASCII 10011011 = e Third generation --"high level" languages Procedural Language -Linear programming -Visual Basic, Java -must define objects and actions Fourth generation --"4GL" languages Closer to data, more like spoken languages -SQL

Select by Attributes

First identify the table (rows) that you will be selecting against

The Earth is Not Round

First the earth was flat -500 BC Pythagorasdeclared it was a sphere -In the late 1600's Sir Issac Newton hypothesized that the true shape of the earth was really closer to an ellipse -More precisely an Oblate Ellipsoid (squashed at the poles and fat around the equator) -And he was right!

Add a Where clause or clauses

Many Operators available here = Equal to <> Not equal to Begin and End with (or Not) Includes values Does not include value Contains text Does not contain text Is and Is Not NULL

Map Scale

Map Scale -Linear (also called graphic) -Verbal 20cm = 4.8km -Representative fraction 1:24,000 -Conversion Example 20cm = 4.8km (original verbal scale) 20cm = 480,000cm (convert all units to a common metric) 1cm = 24,000cm (make the left side equal to one by dividing) 1 / 24,000 or 1:24,000 (remove the unit designation)

Ellipsoid

Mathematical approximation of the shape of the Earth. -The Earth is flattened at the poles and bulges at the equator due to its revolution. -Ellipsoid geodesy is uniquely defined by two numbers: semi-major (a) and semi-minor axis (b). -a > b most commonly used

Primary Key

One per relation (others are alternate keys)

Vector and Raster

Raster: have one value for each grid, can't really represent overlay on top of each other (digital elevation model) Vector : can have any angles (countour lines), faster to process but more complex, harder to analyze The essential difference between raster and vector data formats can be seen in this image. -The contour lines are objects representing elevation, the blue and yellow squares are raster cells representing elevation

Reliability:

Reproducibility of results.

Planar projections

The Earth is projected on a plane. Lots of distortion towards the edges.

Outputting Data

Sharing the results of your geographic labor is one of the primary justifications for spending resources on a GIS. webmapping pdf papaer map , image etc

1. Shapefiles

Simple vector file structure for storing the location and attribute information of points, lines, and polygons. The name "shapefile" is somewhat misleading, because each shapefile consists of at least three files: shapefile.shp, shapefile.shx, and shapefile.dbf. For example, a shapefile containing locations of parks would include the files parks.shp, parks.shx, and parks.dbf. <Shapefile>.shp and <Shapefile>.shx store information about feature geometry. <Shapefile>.dbf is the shapefile's feature attribute table stored in dBASE format. A shapefile can contain only one feature class. Therefore, a park point feature class (representing the park office address) must be stored in a different shapefile than a park polygon feature class (representing the parks boundary). May also include the shapefile's metadata file (shapefile.shp.xml) and the shapefile's projection file (shapefile.prj) Can't represent topological relationships

Types of Attributes

Simple-atomic, non-divisible -Composite-divided into subparts -address -Derived-Age from birthdate -Null-Not applicable Missing -exists Not known -may or may not exist -Key attribute-Value of this attribute uniquely identifies the entity

Learning Objectives

Synthesize basic geodesic concepts -Describe the major elements of the globe and maps -Synthesize the models of the Earth -Understand the difference between the geographic coordinate system and projected coordinate systems -Describe the uses and drawbacks of major map projections -Understand how to measure and visualize distortion from map projections

Learning Objectives

Synthesize database concepts from previous weeksE/R Diagrams to Database Demonstrate concepts of database query Learn how to construct a SQL statementUse Relational Query By Example (RQBE) ArcGIS examples

Categorical (or Nominal)

(SIN, can be #, just a label) -numbers are used as "names" for mutually exclusive sets of objects, events, processes, persons... -different values of the variable do NOT indicate different magnitudes of any property

Layer

feature class or shapefile that is loaded into GIS and participating as a map

Row

Record=instance=Tuple

Visualization

"Worth a Thousand Words" great a picture in mind to better understand the data

Albers Equal Area

-Conic (Secant case) -Well-suited for areas that are mainly east-west in extent -Areas -True -Directions -Reasonably accurate in limited regions -Distances and Scale True only along standard parallels -Map -not conformal -Used for Thematic maps

Distortions

-Fitting sphere to plane causes stretching or shrinking of features

Vector Structure

-Vector GIS are designed around point, line, and polygonal objects and their related attribute data. -This is commonly known as the georelational model

Coverages

-A hybrid data model, often referred to as the georelational model, is used to maintain the connection between features and their descriptive data. -Attributes are related to geographic features by a unique feature identifier (ID) -A coverage is a collection of one or more feature classes.For example, a polygon feature class representing land use areas and a line feature class representing the boundaries between land use types can both be stored in the same land use coverage. Points, lines, or polygons whose coordinates are stored in feature coordinate files Feature coordinate files include explicit listings of feature-ids or arc-ids Unlike shapefiles, more than one feature class may be present in a coverage -This because of topology -Coverages explicitly store topological information (length, area, perimeter, adjacency, and connectivity) as part of the feature attribute table. -One limitation of the coverage data model is that point and polygon attributes cannot be stored within the same coverage.

So, ... what is a RDMBS?

-A type of DBMS that organizes data into a series of records held in linked tables -Aids in data access and transformation because of flexiblelinkages based on record values

Lines

-Also referened to as arcs ( not curved, just two points connected by a line) -Ordered set of coordinate points -Long straight lines links the cordinate pairs -Starting and ending points are called "nodes" -Intermediate points are called "vertices

Relate (ArcGISdefinition)

-An operation that establishes a temporary connection between records in two tables using an item common to both. -An operation that relates two tables using a common field, without altering either table. ex: look up table many to many ex:Relating using the Program_Studentrelationship This creates no new table like a join does but allows access to the data from both parent and child

Raster Analysis

-Analysis in a raster environment involves mathematical manipulation of the values in the cells of the grid. -This analysis can be based on individual cells, or on neighborhood cells -Original data themes (3 layers) to drive data theme (combine into one layer)

Join (ArcGIS definition)

-Appending the fields of one table to those of another through an attribute or field common to both tables. -A join is usually used to attach more attributes to the attribute table of a geographic layer. -JOIN creates a new table

Prime Meridians

-Arbitrary origin of Longitude lines -Usually Greenwich, England -Others include Paris, Bogota, etc.

What can a GIS do?

-Capture data -Store data -Query data -Analyze data -Display data -Output data

Levels of Measurement

-Categorical -Ordinal -Interval -Ratio

Projection properties

-Conformal:maintains shape -Equal-area:maintains area -Equidistant:maintains distance -Azimuthal (Planar):maintains some directions

Lambert Conformal Conic

-Conic (Secant case) -Distances -True only along standard parallels -Map -Conformal but not equal area or equidistant -Area and Shape -Distortion minimal at std. parallels -Directions -Reasonably accurate -Shape -True for small areas -To map large ocean Areas and regions in E-W extent

Ordinal

-Values of the variable only indicate the rank of the measured objects... -Higher values => more of the property, but not how much more

Learning Objectives

-Demonstrate cardinality conceptually and as implemented in ArcGIS -Discuss joins and relates with examplesExplain the difference between Join & Relate -Define Relational Algebra List the 8 Relational Algebra operators

Discrete versus Continuous

-Depends upon the property (concept) being measured, NOT on the nature of the numbers/values of the variablee.g., when we measure lengthin discrete units (1-foot, 2-feet, ...) that does not make length"discrete"

Data Abstraction

-Different vector data types have different options for abstracting real-world entities. -The most common data types and their abstraction options are shown below.

Domains

-Domains (limits)are the conceptual definitions of attributes(e.g. "road class" or "soil type") a named set of values, all of the same type -represent poolsof values from which attribute values are derived -Examples: Valid Tree Species (White Pine, Hemlock, Spruce etc 只有几个选项) or Valid ranges for Annual Precipitation in mm (0-5000).

Keys

-Each relation needs a key -A primary key is an attribute where the value uniquely determines each row in the table. -All attributes or sets of attributes that have the property of row uniqueness are candidate keys -These keys will be evaluated to select a primary key

2 types of datums

-Earth-centered(WGS84, NAD83) -Local(NAD27, ED50)

Entity Sets

-Entity Sets an entity is considered any distinguishable object represented in a database -Entity sets are collections of like entities (groups of instances) -instance of an entity is the same as an occurrence of an entity -an entity is an instance when it is a member of a defined set

Standard Format

-Entity sets and their attributes can be expressed in a standard format -ENTITY_SET_NAME (attribute_1, attribute_2,.... attribute_n) -SOILS (soil_ID, soil_name, perc_rate, color, texture) -Primary keys should be underlined -Best practice in naming is to use and underscore "_" instead of a space

Interval ("equal interval")

-Equal differences in the values of the variable indicate equal differences in the property -Ratios of variable values do NOT indicate equal ratios in the property e.g. C, F, 0 does not mean the absence of heat

Ratio

-Equal intervals in variable values indicate equal intervals in the property, AND -Equal ratios in variable values indicate equal ratios in the property e.g. K, cm elevation if we measure from center of the earth

Azimuthal Equidistant

-Extent -World; Eq/mid-lat/Polar -Distances measured from centre are true; Distortion of other properties increases from centre point -Useful for showing airline distances from centre point -Useful for seismic & radio work

Types of Distortion

-Shape -Area -Distance -Direction

Common Vector Data Formats

-Shapefiles -Coverages -Geodatabases -Triangulated Irregular Networks (TINs) -Grids

Primary Keys

-Should identify only existence and uniqueness -No values should repeat -In our sample table, PARCEL_NUMBER is the best choice for the relation -If no candidate key satisfies these criteria, a primary key should be generated

Sphere

-Simplest (and least accurate) approximation of the shape of the Earth. -The Earth's radius is constant. -a=b

Developable surfaces contacting spheres

-Tangent: projection surface touches sphere -Secant: surface cuts through sphere good for mid-latitude countries e.g.Lambert's Conformal Conic From -No distortion at contact points -Increases away from contact points

Conic projections

-The Earth is projected on a cone. Good for representing parts of the Earth.

Cylindrical projections

-The Earth is projected on a cylinder. Whole-world maps are rectangular. Distortion on the poles.

Modelling Earth's Shape:Why do we need more than one ellipsoid?

-The Earth's surface is not perfectly symmetrical -The semi-major and semi-minor axes that fit one geographical region do not necessarily fit another

Geographic Coordinate System

-The Equator and Prime Meridian are the reference points -Latitude/ longitude measure anglesLatitude (parallels) 0º-90º -Longitude (meridians) 0º-180º -Defines locations on 3-D surface -Units are degrees (or grads) -Not a map projection!

Geodatabase

-The geodatabase is a vector data format that stores point, line, and polygon data in a relational database management system (RDBMS) table. -So far this sounds like a coverage -Like coverages, some geodatabase feature classes have topology. For example, a geometric network has topology and allows you to model connectivity between the features.

Discrete ("variable")

-The propertyis inherently divisible into discrete units, and there are no levels of the property between the units -e.g., number of children is a discrete property of families

Conclusions

-The world must be measured to be of use to us in a GIS -This is not easy:What level of measurement have you achieved? -How accurate, precise, reliable, & valid are your measurements? -How have you simplified a complex world? (analog to digital conversion, etc.) -How does your mental model of the world influence what attributes of objects you choose and how you measure them?

How do we measure distortion from map projections?

-Tissot's Indicatrix (plural: indicatrices) are used to measure and visualize distortions of shape and area at a single location on a projected map relative to a reference globe.

Raster Data

-Trade-off between how closely you want to model reality and file size. -The smaller the cell size, the more detail you can capture. -Larger cell sizes do not require as much disk space for storage but will not capture as much detail. -Raster data can get unmanageablly largeIt is not uncommon to have gigabyte sized files

Validity of Measurements

-Validity of Measurements Reliability is a precondition -Does the measurement system measure what it claims to measureDoes IQ "really" measure intelligence -Determining validity depends upon a good theory/conceptualization of the property being measured

Interval

= and ≠, < and >,+ and -, but no X or /

Ordinal

= and ≠, < and >, no + or -

Ratio

= and ≠, < and >,+ and -, X and /

Multiple where clauses

And vs Or And = both clauses MUST evaluate as true in a single row to return that row Or = if either of the clauses evaluates as true with in a single row, the row is returned

Longitude

Angle from center Earth that describes the east-west position

Latitude

Angle from center Earth that describes the north-south position

Foreign Key

Attribute of a relation which refers to a key in another relation (1:1 or 1:M relationships)

Multi User

Enterprise geodatabaseRequired for multiple simultaneous users Implemented within Relational Database Management System (RDBMS) software Required for archive, replication, SQL querying, multi-user editing

A difference B

A有的， 但B没有的东西

E-R Modeling (part II) -Relationships

Entity sets are expressed as boxes Relationships are shown as diamonds

Candidate Keys

Consider the attributes in the parcel example:OWNER_NAME cannot be a candidate key because values are not unique VALUE cannot be a candidate for the same reason -PARCEL_ADDRESS might be a candidate; addresses can change -PARCEL_NUMBER can be a candidate; its values establish row uniqueness

Large vs. small scale maps

Because it is a ratio, scale is unitlessand large and small scale varies according to project -1:1 is the largest scale -1:24,000 is large scale for Conservation -1:500,000 is a small scale for Conservation -Scale is inversely proportional to area given the same size map (display)

people

Business, government, forester, natural resource management, publichhealth

Categorical

Equality and inequality, no < or >, no + or-

Cardinality

Cardinality defines the numeric relationships between occurrences of the entities on either end of the relationship line

Capturing Data

Digitizing Heads up Tablet Scanning Tabular GPS Downloading

Universal Transverse Mercator

Divides the earth from latitudes 84N to 80S in 60 vertical zones that are 6 deg wide. -Zones are numbered starting at 180thmeridian in eastward direction -Each zone is divided into sections of 8 deg latitude each -Eastings (from Central meridian) and Northings(from equator) can be designated for each zone -UTM preserves Area, Distance and Shape well.

Creating New data with rasters

E.g. digital elevation model,slope model, roughness model (neighbourhood analysis)

SELECT statement

For user's intents and purposes the SELECT statement is often used -The basic structure is as follows:SELECT column(s): Projects FROM table(s):Join WHERE clause(s): Restrict

Procedures

GIS analysis requires well-defined, consistent methods to produce correct and reproducible results.

Raster Strengths

Geographic position is implicit Neighboring locations are represented by neighboring cells Accommodates both discrete and continuous data Analytical algorithms are easy to write Compatible with remotely sensed data

graticule

Geographic/true directions are determined by the orientation of the graticule on the Earth's (spherical) surface. A graticule has meridians (longitude) and parallels (latitude).

Basic GIS Measurement Framework

Geography has a set of "things" (places) and each "has" certain attributes. Thus a simple matrix (cases and variables) serves the model...

Field Based Models (Raster)

Grid of Rows and Columns: Tessellated -Basic Data Unit is spatial (the cell), therefore x,y is implicit -Entity (object) information must be explicitly encoded e.g. elevation

GIS concepts are not new

In the London Cholera epidemic of 1854 Dr. John Snow was able to locate the source of a cholera outbreak by plotting the locations of fatal cases in relationship to nearby wells. Cholera

Examples of Attributes

Lakes:ObjectID, Name, Area, Volume Parks:ObjectID, Name, Area, ContactID Employees:ObjectID, Name, BirthDate, HireDate Municipalities:ObjectID#, Name, Population, Mayor

Examples of Entity Sets and Instances

Lakes:Stave, Pitt, Alouette Parks:Garibaldi, Golden Ears, Tantalus Employees:Bob, Roy, Amy, Gary Municipalities:Vancouver, Surrey, Richmond, Burnaby

Raster structure

Laying a grid on the earth itself (where is ocean and where is land?)

Magnetic directions

Magnetic directions must take into account the compass variation (magnetic declination)

The arcview of shapefile model

Main file (.shp)geometry, Index file (.she) linkage, dBase table (*dbf) attribute info

Latitude/ Longitude

Not uniform units of measure -Meridians converge near Poles -1°longitude at Equator = 111 km at 60°lat. = 55.8 km at 90°lat. = 0 km

Two Broad Model Classes in GIS

Object Based: Treats information space as populated by discrete entities that are geo-referenced Field Based: Treats information space as collections of spatial distributions

Switch back to SQL view to see what you have constructed

Order of operations can be controlled with parentheses () Check "Invert Where Clause" if you want the exact opposite result

h=H+N

Orthometric Height "H": the distance between the earth's surface and geoid Geoid Undulation "N" distance between ellipsoid and geoid Ellipsoidal Height "h" height of earth's surface above or below the ellipsoid

five components of a GIS

People Data Hardware Software Procedures

The arcview shapefile model

Predefined field :(Geometry, object identifier, geometry tracking field)+ custom field (bring in from attribute table)

Mercator Projection

Projected on a cylinder Any straight line is a line of constant direction (rhumb line) Used for navigation -True Directions, -Conformal (angles and shapes true in small areas) but not equal area or equidistant Cylindrical

Intersect

Returns a relation consisting of all tuples appearing in both of two specified relations.

Union

Returns a relation consisting of all tuples appearing in either or both of two specified relations.

Difference

Returns a relation consisting of all tuples appearing in the first and not the second of two specified relations.

Restrict

Returns a relation consisting of all tuples from a specified relation that meet a specified condition. Usually expressed as a WHERE clause. SWHERE City = London row

transverse cylindrical projection surface

Rotate cylinder to reduce distortion along a line -UTM is based on this -Cylinder right angles to the pole

Why Do We Care?

These are important because some operations are not appropriate given levels of measurement

Data

This is by far the most important aspect of GIS -Without data we can't do anything! -Approximate time breakdown of most GIS projects:80% = Database development 10% = Data analysis 10% = Cartographic production

E.F. Codd's 8 Operators

Traditional -Union -Intersection -Difference Special -Restrict -Project -Join

Object Data Structure

Vector data: Points and lines linking points. Points: A single set of coordinates (X and Y) in a coordinate space. Lines: Set of linked points. Polygon : Set of closed lines.

Rasterization

Vector to raster conversion Smooth lines become jagged Areas smaller that the pixel size disappear Mixed pixel problem

GIS data is organized

in Layers

What about a many to many relationship?

look up table, break many to many into one to many relationship *2

A intersect B

他俩一样、重合的部分

A union B

俩表格合一起