GIS Midterm (GEOG 481)

Tobler's First Law of Geography

"Everything is related to everything else, but near things are more related than distant things." (Waldo Tobler 1970)

Conformal Projection

(preserves angles)

data scale

(zoomed in large (data) scale) the scale geographic was collected or digitized at some resolution, which has implications for the map scale at which it can be displayed. Data scale- scale at which the data was collected and the scale at which a map would be most appropriate

GML (Geographic Markup Language) -

- Any vector data common vector data type

John Snow

- demonstrated that visualization of health issues is a spatial problem

Tissot's Indicatrix

- distortion ellipses to help identify what aspect of a projection is preserved and how distortion happens

Jack Dangermond

- president of Esri (makers of ArcGIS)

Michael Goodchild

- we learned about him in Lecture 1. He defined the difference between GIS and GIScience

Euclidean/Pythagorean (straight-line) distance.

-Easy math; can use projected coordinate system coordinates. -Drawbacks: Distance doesn't include topography, Earth's curvature.

Preservation Properties

-Equal area -Conformal (preserves angles) -Equidistant -None (compromise)

COMPONENTS OF SHAPEFILES

.shp, .shx., .dbf, .prj, .xml

advantages of Web Mercator

1. Accurate enough that it can support calculation, e.g. routing vehicles 2. Fast response on calculations 3. Conformal so it preserves local scale 4. Little distortion in areas of high population

Levels of Measurement

1. Nominal 2. Ordinal 3. Interval 4. Ratio

Five Take-Home Concepts of GIS Vector Data

1. Objects have dimensionality 0-dimension (points) 1-dimension (lines) u 2-dimensions (polygons) 2. Attributes describe objects Each object is described in a table Row for each object (called a record) Column for each descriptor (called a field) 3. Vector data is stored as series of points. Lines connect the points, and polygons connect the points with closure. 4. Features are often generalized in a systematic way. More generalization saves cost, but can introduce errors. 5. Vector data utility varies. It is good for working with discrete objects and coordinates, not good for continuous surfaces.

One history of GIS

1963 - Canada Geographic Information System developed by Roger Tomlinson (often called Father of GIS) 1966 - Harvard Lab for Computer Graphics and Spatial Analysis under direction of Howard Fisher created SYMAP. (picture on next slide) 1969 - ESRI Inc. is formed by Jack Dangermond as a consulting firm which performed GIS analysis for clients 1972 - Landsat 1 is launched (satellite) 1981 - ArcINFO is launched by ESRI Inc. 1985 - GPS (Global Positioning Systems) become prime source of data 1988 - US Census Bureau distributes TIGER data 1996 - MapQuest is launched 2000 - GPS becomes fully available for civilian use 2004 - OpenStreetMap is created (what is this-free and editable map of the world) 2005 - GoogleEarth is created 2007 - First iPhone launched which was fully GPS enabled

Ellipsoid

3d, approx the geoid, mathematically defined reg shape -selected and best fited to a geoid

Geoid

3d, approximates sea level, irreg shape

Datum

3d, connects earths surface to the ellipsoid using control points

Geographic Coordinate System

3d, coordinate origin and graticule for specifying locations, latitude and longitude

Earth

3d, irreg shap

Coord conversion: Decimal Degrees to Degrees, Minutes, Seconds

42.086 Keep the full integer as your degree. (42) remainder fraction (60) = 5.16. Keep the full integer as your minutes (5') new remainder fraction (60) ------- 0.16 *60 = 9.6 42 Degrees, 5 Minutes, 9.6* Seconds (*9.6 is smaller than 10 because we started with a rounded decimal degree value)

Coord conversion: Degrees, Minutes, Seconds to Decimal Degrees

42° 5' 10" Keep the full integer as your degree. (42) min + sec/60 -------- (10/60)+ 5 = 5.167 degrees+ updated minutes/60 ------- (5.167/60 ) +42 =42.086117

field

A column in a database table.

Oblique Aspect

A planar or cylindrical projection whose point of tangency is neither on the equator nor at a pole or a conic projection whose axis does not line up with the polar axis of the globe.

COMPOSITE KEY

A primary key that can be derived from two variables that are not unique on their own, but are unique when combined. -(e.g. City field + State field)

record

A row in a database table.

Mercator Projection

A true conformal cylindrical map projection, the Mercator projection is particularly useful for navigation because it maintains accurate direction. Mercator projections are famous for their distortion in area that makes landmasses at the poles appear oversized. Linear scale is constant on the Mercator in every direction around any point, thus preserving the angles and the shapes of small objects and fulfilling the conditions of a conformal map projection. As a side effect, the Mercator projection inflates the size of objects away from the equator.

planar coordinate system

A two-dimensional measurement system that locates features on a plane based on their distance from an origin (0,0) along two perpendicular axes. 2d, corrdinate origin and graticule for specifiying locations, m, ft, etc

map

A two-dimensional, or flat, representation of Earth's surface or a portion of it.

Primary Key

A unique identifier for a row, a column with no repeating values can be a primary key.

Cartographic Scale

Also called map scale, refers to the ratio between distance on a map and the actual distance on the earth's surface. (zoomed out small scale)) Scale on a map is defined mathematically, often expressed as a representative fraction. • Remember it this way: an area appears larger on a large scale map, and smaller on a small scale map. Cartographic scale- the scale of the map with large being zoomed in and small being zoomed out

AutoCAD . DXF (Drawing Exchange Format)

BUILDINGS, LANDSCAPE, CURBS, SIDEWALK, PIPES, ELECTRIC, ETC common vector data type

Manhattan Distance B

Based on the grid-like street geography of the New York borough of Manhattan. The sum of the horizontal and vertical distances between points on a grid

Spatial analysis

Can be thought of as similar to statistical analysis, but including a 2-D coordinate plane. Assumptions of statistical analysis (normality, homogeneity, linearity, independence) are not valid here. Spatial analysis are the steps we undertake to convert raw spatial data into the useful information we've set out to get. -Add value in transformations, which bring out patterns & anomalies. In this class we will talk about 3 types of analysis (there are many moreI encourage you to take GEOG 494 & 495) -Measuring (distance, area, and shape) -Spatial Joins (point in polygon and polygon overlay) -Finding center (centroids, mean & median center, weighted mean center)

Features of a Database Management System (DBMS)

Can store a lot of data Can be accessed through SQL code Table headings should be consistent (underscores, lower case etc.) to allow for joins Data can be entered, retrieved, deleted, edited [In ArcMap: Attribute Table w/ Field Calculator, Edit Session] You can put security features in like passwords, encryption, user accounts You can allow certain users to only view (not edit) Can save a list of edits called versioning u Examples: Microsoft Access, ArcGIS Geodatabases A DBMS is a more generic term than RDBMS. It technically means a database where the data is stored as files and not as tables data stored as files

Nominal data

Categories (no ordering or direction) ex. marital status, type of car owned, counts/frequecy dist,

Spatial Join: Point-in-polygon

Determining whether a point lies inside or outside a polygon It's quite useful to apply areal properties to point locations.

Roger Tomlinson

Developed first GIS

Interval Data

Differences between values can be found, but there is no absolute 0. (Temp. and Time) ex. temp in F, standardized exam score counts, freq of dist, mode, median, order of values is known, quantify the diff between each value, add or subtract values,

Referential Integrity

Ensuring that users specify certain data types (e.g. no letters in a zip code field)

Benefits of Vector Data

Features can have associated attributes. Discrete objects can be shown Deleting, creating, modifying is relatively easy (e.g. a new park). Better geographic accuracy because we don't have to choose a grid size - Good for precision. Attribute table works well with database systems (columns and rows). Can create routes and networks

Waldo Tobler

First law of geography

GIScience

Geographic Information Science "The science of the systems"

GIS

Geographic Information Systems Geographic - relates to a specific place on or in relation to the Earth's surface Information - is data to which some value or interpretation has been added. In GI, the information relates to measurements, maps, images, sounds etc. of the Earth's surface Systems - a system designed to perform a wide range of functions on and with GI

KML or KMZ (Keyhole Markup Language )

Google-owned. - Any vector data. common vector data type

spatial join vs attribute join

Join by location or spatial join uses spatial associations between the layers involved to append fields from one layer to another. Spatial joins are different from attribute and relationship class joins in that they are not dynamic and require the results to be saved to a new output layer.

Latitude

Lines of latitude are parallel to each other. (called parallels) The length of latitude lines decreases closer to the poles measured in degrees Degrees, Minutes, Seconds Decimal Degrees

Longitude

Lines of longitude converge at poles (called Meridians) measured in degrees Degrees, Minutes, Seconds Decimal Degrees

Vector

MATHEMATICAL EQUATIONS (points, lines, polygons) • Mathematical equations translated into points that are connected by either lines or curves • Volume of data depends on number of vertices • Often used for human and environmental data • Resolution is variable

Mean Center (points)

Mean- Identifies the geographic center (or the center of concentration) for a set of features.

median center

Median- Of all the features, which one most closely falls in the center of the X & Y coordinates of all features (median).

.xml

Metadata for ArcGIS—stores information about the shapefile.

no preservation properties

None (compromise)

Subtypes and domains

One way to ensure referential integrity is to use subtypes and domains in your database These allow ease of use for those inputting the data, avoid errors Can limit types of data inputs

Open Data / Open Source

Open data is data which is open to public use Open source refers to technology where the source (code) is open to be used to create new technology or improve the current technology

OpenStreetMap

OpenStreetMap is a map of the world, created by people like you and free to use under an open license.

Raster

PIXELS • Loses image quality as you zoom in • Volume of data depends on cell size • Often used for remote sensing and imagery • Fixed resolution

RDBMS

Relational database management system (what does relational mean?) GIS uses RDBMS where tables are used to store data. Traditional RDBMS are not good for all data. Raster data, Long text (books, etc.), Images), Origin/destination (network data) data stored as tables

Network distance

Requires special dataset(s): topology, traversal rules. Holy grail of online navigational maps

select by location

Selecting based on how the layer interacts with other layers - do proximity anaysis

Great circles

Shortest distance between two points on the earths surface

Spatial Join: Polygon overlay

Similar to point-in-polygon, as two objects are involved. Combination of two or more sets of features, essentially creating a new set of features. Geometry is 'split' to define the spatial extent of the combinations.

Ellipsoid, Major Axis, Minor Axis & Flattening

Spheres are defined by a radius from their centers. Ellipsoids are defined by two axes: Major and Minor u Flattening is a ratio showing how flat the ellipsoid is as compared to a sphere. u WGS84 - World Geodetic System of 1984 u NAD83 - North American Datum of 1983 is almost identical but is highly accurate for North America

Attribute data type: Geometry

Technically, the geometry of the feature is itself an attribute that can be queried. Spatial is special, though, so sometimes this point gets smoothed over. Alt name: geom, shape. This attribute is written: point, polyline, polygon

attribute types

Text, Numeric, Boolean, Data/Time, Geometry

Military Mapping Maidens- WW2

The "Military Mapping Maidens" - or "3Ms" - charted strategic locations, churches, schools, land contours, bodies of water and roads. They used foreign maps, aerial photos and other information to create the maps. Some were printed on silk and carried by troops as survival tools.

TIGER data

The Topologically Integrated Geographic Encoding and Referencing system (TIGER) data, produced by the US Census Bureau, is a public domain data source which has many geographic features. The TIGER/Line files are extracts of selected geographic information, including roads, boundaries, and hydrography features.

.prj

The file that stores the coordinate system information. Used by ArcGIS.

Relational Algebra- Queries using Logical Operators (AND/OR)

Underpinning of how query languages for databases Defines how relations (i.e. tables) can be manipulated and queried Think of Venn Diagrams

Overlay

Union Intersect Clip Erase Split Select by Location doing some operation which relies on the layers overlapping u

John Snow

Using maps to do analysis and solve problems -cholera water pump

Attribute data type: Numeric

Value is a number. Two main numeric types: -integers: whole numbers with no fractions, Example: -11574, Alt names: int, bigint, tinyint, long, short. - floating point: numbers with fractions, Example: 4387.112, Alt names: float, double, numeric. Can be nominal, ordinal, interval, or ratio

Attribute data type: Date/time

Value is a representation of a date, time, or both together. Example: 2012-06-06 20:03:00 (how stored in format is complex) Alt names: date, time, datetime. Dates & date-times are interval, but not ratio. Times are ratio only if they're stored as 24-hour style.

Attribute data type: Text

Value is a sequence of characters, including letters, numbers, punctuation, whitespace, Example: 'Knight Library' Alt names: string, char(acters). Generally nominal. Can be ordinal, but system would not automatically recognize order outside of alphanumeric order.

Attribute data type: Boolean

Value is one of only two possible values: True or False. Alt names: bool Technically nominal, though one could insist that True is 'more than' False (ordinal?). Most GIS logical data models have no explicit boolean attribute type. Substitutes: Integer: 0 = False, 1 or any other value = True (programmers prefer). Text: 'N' = False, 'Y' = True (or any similar design) (users prefer).

Raster vs Vector

Vector data are excellent for capturing and storing spatial details, while raster data are well suited for capturing, storing, and analyzing data such as elevation, temperature, soil pH, etc. that vary continuously from location to location. Raster data formats also are used to store aerial and satellite imagery.

figures in the history of GIS

Waldo Tobler- First law of geography Roger Tomlinson- Developed first GIS John Snow- demonstrated that visualization of health issues is a spatial problem Jack Dangermond- president of Esri (makers of ArcGIS) Michael Goodchild- we learned about him in Lecture 1. He defined the difference between GIS and GIScience

Spatial' attribute join

When output combines dataset attributes, can be thought of as a spatial version of a join: joining datasets using the geometry as the key-field. -By the complex nature of geometry, has to use different method for linking than dataset1.key = dataset2.key. -The method by which the geometry are related is the analysis. Example: Using a base feature class with cities' economic information; want to add some state-level info, e.g. unemployment.

Drawbacks of Vector Data

You aren't guaranteed to describe a surface, not great for continuous data that has gradual variation. There is little uniformity in the shape size, so areas and distances have to be calculated. When preforming overlay analysis polygons may not completely line up. -This leads to something called "silver polygons". In our labs we try to avoid you running into these problems, but just know that overlays aren't perfect in vector land

SQL (Structured Query Language)

a special purpose programming laungage designed for managing data help in a relational database mangemnt system SELECT * FROM mytable WHERE nation = UK SELECT nation, COUNT(treetypes) as treespeciesvariety, FROM mytable WHERE treetypes = elm The query tools in ArcGIS only concern themselves with the where clause part of an SQL query. The SELECT * FROM dataset WHERE part is conveniently taken care of for you

null value

absence of recored value shapefiles not allow null values

dissolve

aggregates features based on specified attributes

append

appends multi inputs into existing target dataset (use merge to make new output data set)

Attribute join

based on common attribute field No change in geometry of layer temporary. make permenat by crease new output of compnenet one to one or many to one

proximity

buffer select by location describes operations that are looking at two layers which may be close but not necessarily overlapping u -We do a buffer to find an area that is within an distance of our layer of interest -We then do an overlay to see how that buffer overlaps with other layers

cone

class good for mid latitudes

Cylinder

class often good for whole earth projections

Plane/azimuthal

class good for local areas

Taxonomy of Projections

class, aspect, case, line/point of tangency, distortion properties

translating Nominal to Ordinal

colors to assigned value rankings - simplfy calcuations

developable surfaces for projections

cone, cylinder, plane

North Arrow

correct in image A north arrow only works on the cylindrical projections! (or on central meridian of a conic projection, but that requires putting the north arrow right in the middle of the map)

.dbf

dBASE table that stores the attribute information of features. Required. There is a one-to-one relationship between geometry and attributes, which is based on record number. Attribute records in the dBASE file must be in the same order as records in the main file.

Ratio Data

diff between measurements with true 0 ex. height, age, weekly food spending counts, freq of dist, mode, median, order of values is known, quantify the diff between each value, add or subtract values, can multiply and divide values, has true 0

clip

extracts input feature that overlay the plip features -cookie cutter to use on another featuer class

interesct

featuers pr portions of feature whihc over lap in all layers will be output

definition query

features not returned are excluded from applicatins interfact, limits ap and analysus but not delete underlaying data

entitiy

first column

attributes

first row that tells what measuring

instance of ------

first value in a row

union

geometic union in input to crease into 1 output feature class

.shx

index file that stores the index of the feature geometry. Required.

Aspect

its orientation on the page or display screen.

coordinate systems

let us points in continuous space and measure spatial properties (e.g. distance) -sphere coordinates - angles -cartesian coordinates - distance

TIGER (Topologically Integrated Geographic Encoding and Referencing)

line files. -STREET NETWORK common vector data type

.shp

main file tores feature geometry. required

Projection

math transformation to convert 3d shape to 2d

Centroid of a polygon

mean of unweighted coordinates

qualitative data

measuring of differences not quantities. non numeric. ex. written text, experiences, emotions, descriotions

Quantitative data

measuring of quantity of something. Numerical. ex. measurements, ratings, things that can be counted.

erase

opp of clip

ordinal data

ordered categories (rankings, order, scaling ex. service quality rating, student letter grades, counts/freq of dist, mode/media, order of values is known

GIS Operations

overlay and proximity

Weighted Mean Center

patial equivalents to the statistical mean and standard deviation Center is 2-D equivalent of mean: a weighted average of X & Y coordinates represented by a point. Mean center of values (U.S. population): The values add 'weight' to the coordinates.

Tangent

standard line or 1 standard point have a standard point

nature of geographic information

taking the world and organizing it so we can analyze it with a computer

case

tangent vs secant The standard line is where the projection is correct. As you move away from the standard line, you get distortion.

compactness

thinness - how compact or spread-out (thin) a polygon is. Generally, a relationship between the perimeter and area. e.g. (4π*area)/(perimeter²) (1 = perfect circle, (approaching) 0 = ever more line-like).

Secant

two standard lines, which means there are two places where the projection has no distortion 2 standard lines or one standard circle (secant) Secant projections have a standard circle (on plane) It is distorted as you move away from the standard lines, no matter which direction. More distortion happens the further you move from the standard line(s)

great circle (geodesic) distance

way of measureing distance

The standard line

where the projection is correct. As you move away from the standard line, you get distortion.

What does GIS help us do?

• Create maps for navigation • Identify areas of vulnerability from flooding or other disasters • Decide on site locations for a new housing development • Predict landslides based on geomorphological processes • Identify where to locate a store where it can be most useful to potential patrons • Create historical maps by georeferencing old maps to current coordinates • Identify the easiest path to traverse across an area