GIS 1
Universal Polar Stereographic (UPS) coordinate system
A map projection of the earth onto a cone so that one of the poles is the most accurate part of the map (Northing and Easting)
Transverse Mercator
A map projection of the earth onto a horizontal cylinder so that the Prime Meridian (or some 6 degree UTM zone strip) is the most accurate part of the map
Mercator projection
A map projection of the earth onto a vertical cylinder so that the equator is the most accurate part of the map
What are the characteristics of the spaghetti vector data model?
A spaghetti model is a compilation of lines that are not yet constructed into polygons, meaning that they have no relation to each other yet (No spatial topology)
Spatial query
A special type of database query that allows for the use of geometry data types (points, lines, and polygons) and consider the spatial relationship between these geometries.
Map projection
A systematic transformation of Lat & Long onto a plane surface (Northing and Easting) -Different types of projection, some are better than others for certain areas of the globe -Distortion is inevitable
Advantages and Disadvantages of ASCII Coded binary representation
A: -coding characters -easily readable (with a text reader) D: -slow -takes up more space
Edge-matching
Adjusting the positions of features which extend across map sheets so that the parts of the features match i. Determine the base layer and the target layer (to be edited) ii. Define the area to be matched (Link area) iii. Identify the links in the area iv. Perform adjustment v. Repeat the process if some areas are not matched
Why do we use statistical Affine Transformation to perform coordinate transformation? What is the basic idea? What is the critical element in statistical Affine Transformation?
Ahh
Given a TIN diagram, construct the Triangle-Node table. Where would one store the elevation data and the x-y coordinates for each node?
In the node attribute table
What is a linear time model and what is a cyclical time model?
Linear model is represented in a line form, where as a cyclical time model is represented in a circle that is endless. (chicken to egg example)
Compare and contrast the three basic spatial data models (raster, vector and TIN).
See screenshot
Objects vs. Fields
Two aspects of conceptualizing spatial variation. Objects: Entities with explicit boundaries and attributes. Fields: Attributes varying over space, no explicit boundary. *The most fundamental dichotomy in perceiving the world!
Abrupt variation vs Continuous variation
Two aspects of spatial variation. Abrupt: buildings, roads, and land use types. Continuous: elevation, precipitation, temperature.
Ratio data type
Values indicate explicit numerical difference, with non-arbitrary zero point -Quantitative -Ex: height -Ex: weight -Ex: distance
Interval data type
Values indicated explicit numerical difference, with arbitrary zero point -Quantitative -Ex: temperature -Ex: grades
Ordinal data type
Values involve ordering/ranking of the data -Qualitative -Ex: high, low -Ex: small, medium, large
Nominal data type
Values involving grouping, but no ordering ("name") -Qualitative -Ex: red, blue green -Ex: forest, agriculture, urban
What logical model is used for an objects conceptual model?
Vector Data Model -As distinct objects -Uses lines and vertices to make polygons to form the objects
Raster Data Model
a conceptualization of representing spatial data with a series of equally spaced and sized grid cells -Continuous spatial variation (fields)
Line segment
a straight line connecting two vertices
Should you use latitude/longitude as coordinates when registering a digitized paper map? Why?
Yes, because the intersections of the grid make definitive points that are already labeled with X and Y coordinates, so it is easy to input those values.
How do you refine control points in statistical Affine transformation?
You have to calculate coefficients and errors. Check your RMSE and if it is too large then delete points that might be off.
Quad tree Encoding (Practice exam, lec 6)
You need to make four homogenous quads, so if you can't then you would lose detail. So in order to not lose detail, you can only use this if it is naturally divided into quads (by feature).
What is Quadtree? What is the problem with this data model?
You need to make four homogenous quads, so if you can't then you would lose detail. So in order to not lose detail, you can only use this if it is naturally divided into quads (by feature).
How to store thematic attributes associated with each object?
You will have two (or more) tables with information about the object. You will want to join the tables together to make it easier to read. In order to do this, you must find a common field. Use this common field to join the tables together temporarily. Then add new fields to permanently add the rest of the fields from the second table. Use the filed calculator to make these new fields equal to their respective fields from the second table. ***You must also make sure the Operator Value is the same for common fields***
The Mixed Pixel Issue
[Raster Model] Inside certain pixels there are more than one land cover types. -This depends on the size of the pixel. (Level of spatial details depends on the size of pixel)
Objects
Entities with explicit boundaries and attributes -Used for conceptualizing spatial variation in a vector model
Remember when encoding raster data that the first block/pixel in the square has coordinates _(___,___)__
(0,0)
LiDAR
(Light Detection And Ranging): record the surface of the earth, by illuminating earth surface with a laser and analyzing the reflected light.
Thematic Attributes description and examples
(What it is, what the properties are) Ex: spatial distributions of 10 ecosystems services in the Yahara Watershed, WI, for 2006. --includes maps that show crop production, pasture production, freshwater supply, forest recreation, hunting, flood regulation, water quality, etc.
How is 11 represented in a binary system using the Direct binary representation method and how is it represented using the ASCII method?
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What are the advantages and disadvantages of data representation using the ASCII method?
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What is spatial topology? How is it captured in GIS?
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What is the difference between a categorical attribute and an ordinal attribute?
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What is the main difference between an ordinal attribute and an interval attribute?
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The Geoid
- is an equipotential surface most nearly approximating the earth's surface
Elements of a Raster Data Model
-Cell (pixel) Value -Cell (pixel) Size -Raster Bands (layers) -Spatial Reference
Advantages of a Vector Model
-Data can be represented at its original resolution and form without generalization. -Graphic output is usually more aesthetically pleasing (traditional cartographic representation); -Since most data, e.g. hard copy maps, is in vector form no data conversion is required. -Accurate geographic location of data is maintained. -Allows for efficient encoding of topology, and as a result more efficient operations that require topological information, e.g. proximity, network analysis.
Benefits of encoding spatial objects in topological vector model
-Enable topological editing (avoid topological error) --Allows editing of sliver polygons, overshoots, and undershoots -Smaller file size --Shared vertices of adjacent polygons are not stored twice -Enable network analysis --Ex: urban network analysis
Database View (of GIS)
-GIS as a giant spatial database -A view held by computer scientists -Focus on spatial data management
Spatial Analysis View (of GIS)
-GIS as a set of tools for analyzing spatial data -A view held by quantitative geographers -focus on the analysis of spatial data
Map View (of GIS)
-GIS as a way of starting and making maps -A view held by cartographers -Focus on the visualization of spatial data
The four aspects of Geographic Information:
-Location (Where it is) -Spatial Topology (How is it spatially related to other things) -Time (When it happens and how long it lasts) -Thematic Attributes (What it is and what its properties are)
TIN model
-Perceive the world (a surface) as continuous but definable facet -Represent the surface of an area with an array of non-overlapping triangular areas -Triangle is the basic spatial unit. Each triangle represents a facet of the surface -The area covered by a triangle is assumed to be uniform in its changes -Each of the three edges represents the change of one uniformity into another
Describe the topologies of any pair among Science Hall, Memorial Union, North Park Street, and UW Campus.
-Science Hall and Memorial Union within UW campus. -Park St crosses UW campus -SciHall is disjointed from Park st.
Disadvantages of a Vector Model
-The location of each vertex needs to be stored explicitly. -For effective analysis, vector data must be converted into a topological structure. This is often processing intensive and usually requires extensive data cleaning. As well, topology is static, and any updating or editing of the vector data requires re-building of the topology. -Algorithms for manipulative and analysis functions are complex and may be processing intensive. Often, this inherently limits the functionality for large data sets, e.g. a large number of features. -Continuous data, such as elevation data, is not effectively represented in vector form. Usually substantial data generalization or interpolation is required for these data layers. -Spatial analysis and filtering within polygons is impossible
Affine Transformation
-a linear mathematical process by which data can be altered to align with another data source - differential scale, skew, rotate, shift data (needs THREE control points)
Break lines
-lines which help define and control surface behavior in terms of smoothness and continuity --hard break lines represent a discontinuity (an abrupt change) in the slope of the surface (streams, roads, etc) --soft break lines allow you to add edges to a TIN to capture linear features that do not alter the local slope of a surface
Mass points
-points with height measurements, which help determine the overall shape of the surface -well-placed mass points occur where there is a major change in the shape of the surface --the peak of a mountain, the floor of a valley, the edge (top and bottom) of cliffs
Hulls
-polygons which represent surface features with area, such as lakes, or boundaries of those surface features (the shores of individual island, or the boundary of a study area)
Characteristics of vector data model
1) Geographic features are treated as individual objects, represented by points/lines/polygons. 2) The spatial boundary of an object is explicitly and accurately coded (as coordinates of points); 3) Ahribute data are stored in relational databases and connected to spatial objects; 4) Spatial topology among features can be explicitly coded; 5) Compacted spatial data model (compared with raster) 6) Complex data structure 7) Require expertise when used for spatial analysis
Creation of a TIN model
1. Choose mass points 2. Define break lines and hulls (more control over the shape of the TIN surface) 3. Creating triangles based on mass points in each sub-area defined by hard break line
Important issues associated with representing GI
1. Selectiveness (Can we represent EVERYTHING in the real world? Sometimes things need to be simplified) 2. Scale of representation (How detailed do we intend to represent the real world? aka map scale) 3. Spatial auto-correlation [spatial dependency] (Tobler's first Law of Geog.)
Simple Affine Transformations
1. Translation 2. Rotation 3. Scaling 4. Shearing/Skew
Projected Coordinate System
A 3D GCS projected onto a 2D flat surface (to make a map)
Delaunay Triangulation Approach
A circle drawn through the three nodes of a triangle will contain no other node
What is datum in terms of coordinate system? Should we always need a datum in defining a geographic coordinate system/projected coordinate system? Why?
A datum uses positioning locations and defining measurements on the surface of the best fit ellipsoid (for the earth) to act as a base for a geographic coordinate system. Yes, because we need some ellipsoid to act as the ideal shape of the earth. Without one the earth would be too irregular for us to have a reliable algorithm that applies to the whole planet (or even to one area in some cases).
What is a GCS? What is a PCS? What is the main difference between them?
A geographic coordinate system is global reference system that uses latitude and longitude to define the locations of points on the surface of a sphere or spheroid (Earth). A projected coordinate system is a 3D GCS projected onto a 2D flat surface to make a map. This system uses different measurements that can be calculated from the GCS, but are not always accurate to the earth (due to distortion when projecting). The main difference is that a GCS is based on the real world, where as a PCS is a projection, so it will always have distortion at certain areas of the map.
Geographic Coordinate System
A global reference system that uses latitude and longitude to define the locations of points on the surface of a sphere or spheroid (Earth). (Ellipsoid, Datum)
Compare and contrast the representation of digital elevation data using a raster data model and that using a TIN model
A raster data model shows elevation using different colored areas of pixels. A tine model uses mass points, breadlines, and hulls
Raster Bands (Layers)
A raster may have a single band or multiple bands. Each cell in a multiband raster is associated with more than one cell value.
What is a relational database? What are the key data structure elements for such a database? How is it used in GIS as part of vector data model?
A relational database is 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. The key elements: points, lines, polygons. A relational database is used in GIS to create a vector model by combining the elements to form objects, that are then stored in relation to each other, creating spatial topology.
Exhaustive search
A search for information in which each item in a set is examined, even after the target is found. -Considers all possible solutions
Binary search
A search in which, at each step of the search, the set of data elements is divided by two, then the half is chosen that the searched element is in until the searched element is found.
What is binary search? How is it is different from exhaustive search in terms of its requirements on the table to be searched?
A search method that involves cutting the dataset in half repeatedly to find the desired search object. It is different from exhaustive search because the binary search only looks at the halves of the table that contain the desired search object, but the exhaustive search looks at every single part of the table, even if the desired search object is already found.
What is a spatial data model?
A set of constructs for representing and processing GI in the digital environment of computer (An abstraction of real world)
Difference between a node and a vertex
A vertex is a shape point, and a node is a point at the intersection of two or more lines
Region topology
Area features can overlap with other area features
Polygon topology
Area features can share boundaries
Fields
Attributes varying over space, no explicit boundaries -Used for conceptualizing spatial variation in a raster model
Why would people say when TIN is used to represent a terrain surface, it captures the structure of the surface?
Because it shows elevation, streams and roads, and soft changes
How does a vector data model represent spatial data? How does it represent a point feature, a linear feature, and an area feature?
By showing objects with abrupt boundaries. A point is represented with a point, a linear feature is a line, and an area feature is a polygon with a boundary.
Selectiveness as an issue associated with representing GI
Can we represent EVERYTHING in the real world? -Sometimes things need to be simplified --Ex: a drawing of Custer's battle showing only Custer's army on horses vs the NA's on foot. -Throw away/ignore info that only applies to a small area -If certain info remains constant over space, you can just keep it collected at one location and ignore the others -The hierarchy of importance Things that can be the emphasis of a map: roads, parks, buildings, etc.
9-Intersection Model (9IM)
Characterizing the spatial relationships between any pair of basic elements by examining whether the nine possible intersections between interiors (I), boundaries (B), and exteriors (E) are empty (F) or not empty (T). (See screenshot for an example)
What is a datum?
Datums provide the basis for positioning locations and defining measurements on the ellipsoidal surface. A datum begins with a best fit ellipsoid, then establishes a set of accurately measured points for which horizontal and vertical positions are accurately determined.
Vectorization
Conversion of a raster data model to a vector data model
Rasterization
Conversion of a vector data model to a raster data model
Polygon (vector model)
Coordinates of a loop of points defining the boundary of the polygon
Line (polyline) (vector model)
Coordinates of a sequence of points defining the shape of the line
Point (vector model)
Coordinates of the point (x, y)
Creation of a TIN Model
Creating triangles based on mass points in each sub-area defined by hard break line -Delaunay Triangulation Approach
Heads-down digitizing
Digitizing vector features from a map mounted on a tabular digitizer Key Processes: 1) Digitize reference points (corner points) on the map document; 2) Define and digitize control points; 3) Tracing features on the analog map (stream mode / point node.)
Block Encoding (raster)
Divide map into blocks by section/theme. -blocks must be square and contain only pixels of the same theme. -Try to have the least amount of blocks possible. (0,0,4,A) ---Means that the coordinates for the first pixel of the block section is (0,0), it is 4 pixels long (and deep, bc its square), and it is theme A.
Cell (pixel) Value
Each cell in a raster carries a value, which represents the characteristic of a spatial phenomenon at the location denoted by its row and column
Are distances given on a plan on a projection or just on the ellipsoid?
Ellipsoid
Spaghetti Model
Entity by Entity -A vector model that stores features as independent objects that are unrelated to each other. Think of dropping a handful of spaghetti onto a plate. The spaghetti strings overlap and cross each other, but each string is completely independent. -Spatial objects (points, lines, polygons) are encoded one by one without spatial topology defined -Each point, line, or polygon is stored as a record in a file that consists of that entity's ID and a list of coordinates that define geometry.
Spatial relations of the different elements
Equal Disjoint Intersect Touch Overlap Cross Within Contain
True or False: The Earth is perfectly round.
FALSE
What is the dichotomy in perceiving the world? How is spatial variation of geographic information perceived under this dichotomy? What are the spatial data models for representing spatial data under this dichotomy?
Fields and objects. Fields are continuous land types with no harsh boundaries (continuous variation), where objects are distinguished polygons (abrupt variation). Fields are modeled with raster models and objects are modeled with vector models.
Full Raster Encoding
Full representation, no compression -If a pixel is theme A, then you will code that pixel as A in the table
GPS
GPS satellites broadcast signals from space, and each GPS receiver uses these signals to calculate its 3D location (latitude, longitude, and altitude) and the current time
ASCII Coded binary representation
Good for characters -Data (in characters) is first converted into ASCII code character by character. -Each ASCII code is then coded into binary representation. -Need to use the ASCII table to see what certain characters stand for (I think)
The four components of GIS:
Hardware Software Data People
Scale of Representation as an issue associated with representing GI
How detailed do we intend to represent the real world? -Map scale = Distance on map / distance on the ground -different ways of representing scale (different units or keys on a map) Small scale will be from farther away, large scale will be more zoomed in, like on a city
Ellipsoid
Ideal shape used to approximate the shape of the Earth
Three parts of a basic element:
Interior, Boundary, Exterior (The boundary of a line are its two endpoints)
What are the best data types for representing a Formula One Race?
Interval: first place to last place
10.
Is a datum, not a projection (NAD 83 is a datum)
What does a map projection do? What are the main advantages provided by map projection?
It projects the 3D globe onto a 2D surface. This helps to see the whole Earth at one time for learning purposes, navigation, etc. It is also easier to carry around a 2D map than a whole globe.
Node topology
Line features can share endpoint vertices with point features
Arc-node topology
Line features can share endpoints
Route topology
Line features can share segments with other line features
Point directory method
Listed by point, and which polygons it is a part of ***Preferred method because no data redundancy ***
Geo-referencing
Local (Arbitrary) Coordinate System --> Projected Coordinate System (real-world coordinates) 1. Collect control points at which BOTH local coordinates and real world coordinates are known 2. Calculate coefficients and errors 3. Refine control points "Create a "compromised version" that best fit all control points statistically"
Node attribute table
Location & Attributes -Lists the nodes and their coordinates and what elevation they stand for
Heads-up digitizing
Manually digitizing vector features from a scanned image on computer screen Key Processes 1) Load scanned image 2) Georeferencing the image (geo-registration) 3) Place vertices on screen to define point, line and polygon objects (point-mode/stream-mode)
The three views of GIS:
Map view Database view Spatial analysis view [Visualize : Manage : Analyze] --These three views are usually combined in a GIS system
Conflation
Matching features between different source datasets so as to retain accurate data, minimize redundancy, and reconcile data conflicts. i. Identify the base layer ii. Specify the area to be conflated iii. Establish the links between the two layers iv. Perform adjustment v. Repeat until satisfactory
Encoding a TIN
Node attribute table Triangle-Node table
Four major types of Attribute Data
Nominal (Qualitative) Ordinal (Qualitative) Interval (Quantitative) Ratio (Quantitative) Other types: cyclical, counts
What are the best data types for representing books on a shelf?
Nominal: by subject Ordinal: size ? Interval: Alphabetical Ratio: Chronological
One datum is an ellipsoid, but one ellipsoid can be assigned multiple datum.
One datum only has one corresponding ellipsoid
Other coordinate systems besides WGS 84 (a GCS) and UTM
PLSS Zipcode
Point events
Point features can share vertices with line features
Simple lists method
Points listed by polygon ***Data redundancy; Difficult for maintenance***
Control Points
Points whose coordinates are known in BOTH coordinate systems -Used to geo-reference maps -You want four or more. The more points, but you want a balance between cost and accuracy (don't want too many points)
Pros and Cons of TIN Model
Pos: a) compact, no redundancy b) facilitate the computation of surface attributes (slope, aspects, etc), easy to represent the structure of a surface Cons: a) many possible triangulations from a same set of points b) slow to create c) difficult for spatial analysis operation (almost impossible for overlay)
Geographic data collection
Primary geographic data Secondary geographic data
Pros and cons of satellite and aerial photograph data (primary sources)
Pros: -consistency and efficiency -mapping inaccessible areas -up to date info Cons: -restricted by cloud cover -high cost
Pros and Cons of Spaghetti Vector Data Model
Pros: -simple -efficient for display and plotting Cons: -inefficient for most types of spatial analysis
Pros and cons of ground surveying
Pros: -the best way to obtain highly accurate point locations Cons: -very time-consuming and expensive
Pixel is the basic unit of the _____ model
Raster
What logical model is used for a fields conceptual model?
Raster Data Model -As continuous fields -Uses pixels
Which model is best used for themes that continuously vary over space? (eg elevation, temp, precipitation...)
Raster data model (pixels)
Spatial Reference
Raster data must have the spatial reference information so that they can align spatially with other data sets in GIS. Usually, the number of rows, number of columns, cell size, and area extent (lower-left and upper-right corner) expressed in UTM are recorded.
Secondary geographic data
Raster: -Scanned maps, photos, publications Vector: -Vectorized topographic maps -Place-name databases
Primary geographic data
Raster: -satellite images/remote sensing -Digital aerial photos Vector: -Field survey measurements -GPS measurements -LiDAR
Local (Arbitrary) Coordinate Systems
Real-world coordinates (Lat&Long in GCS, Northing and Easting in PCS) -For a Local Datum
Relational Database (thematic attributes of point, line, and polygon) -Structure of a table
Record: a row of a table. Each record represents a unique object (point, line, or polygon) Attribute Field: a column of a table. "Field Name", "Field data type" and "Field width" must be specified for each field. A primary key column is used to uniquely identify each record.
Binary Coding
Represented using a system of 1s and 0s (on/off) -used in computers to reduce file size -Is a system of base two -good for numbers -Bits an bytes
What are the ways to compress raster data?
Run-Length Encoding (Standard, From-To, Value Point) Block Encoding Quad-tree Encoding
Review question 26. Steps for something
Show that you understand how to follow info from one column to another. -find a common field from one table to another 1. determine what boarders the river by looking at the arc topology table so you can see how the boarders of the homestead you're looking at relates to the river. 2. look at the polygon table 3. transfer that to the parcel labels 4. then you can see the boundaries 5. find the land owners that boarder the river 6. then average out what I'm trying to find (the average income) -follow what the computer would do. Find what polygons i need, which arcs of those polys boarder the river. Find the owners of the polygons, then find the income of those owners and average them.
Types of Affine Transformations
Simple Complex Statistical
Encoding methods for spaghetti model
Simple lists method Point directory method
What are the two methods to encode spaghetti vector data model? What is the main difference between them?
Simple lists method Point directory method -Point directory is preferred because it doesn't have data redundancy. Simple lists method lists every point that is part of a polygon for every polygon, so points that are shared by multiple polygons are listed multiple times. Makes it difficult for maintenance.
Everything is same database?
So everything is together, like all your feature classes. It helps to keep all your FCs in the same coordinate system
Why can I read some files using MS notepad but not others?
Something about having or not having a text reader, which is needed to read data is ASCII?
Triangle-Node table
Spatial Topology -lists the triangles, their nodes, and neighbor triangles
Spatial Topology (description and types)
Spatial topology studies the geo-spatial relationships between geographic objects. Types: -arc-node topology -polygon topology -route topology -region topology -node topology -point events
How do you model a spatial data model?
Spatial variation: Abrupt variation vs. Continuous variation Conceptual model --> Conceptualizing spatial variation --> Objects and Fields ---The most fundamental dichotomy in perceiving the world!
What are the criteria in choosing initial control points (where, how many, spatial distribution)
Start with three points that are pretty far apart, then try to distribute them easily as you go. You want enough points to ensure accuracy, but you want to find a balance between cost and accuracy. Too many points can be bad.
How to make a TIN model:
Take the triangle, then cut those lines in half. Each triangle is a constant change in elevation. You get the actual elevation from the
Cell (pixel) Size
The cell size determines the resolution of the raster data model. A cell size of 10 meters means that each cell measures 100 square meters (10 X 10 meters)
Universal Transverse Mercator (UTM)
The division of the Globe into UTM Strips (Zones) -60 UTM in total -6 degree strips -Apply a secant transverse mercator proaction to each UTM zone (Northing and Easting)
Geo-coding
The process of assigning a coordinate value to an address by comparing the descriptive location elements in the address to those present in the reference material 1. Prepare reference data (ex: detailed street map) 2. Locate address (Common approach: linear interpolation with known address)
What do you model in a spatial data model?
The four aspects of GI: Location, Spatial topology, Time, and Thematic Attributes
Base 2 Principle
The relationship between bit position and the magnitude of value -8 boxes, 0-7 -These boxes are either filled with a 1 or a 0, which will in turn represent a number based on which box they're in. -This can add up to 211. After this they need to add more bytes.
Global Datum
The spheroid matches the earth surface closely in different parts of the world (Best fit globally)
Vector Data Model
The world is perceived as distinct objects represented by points, lines, and polygons
9.
They are not the same because they use different datums that the projections are derived from.
Describe the design of UTM coordinate systems.
They divide the earth into 60, 6˚ sections, called UTM Zones that run from the North Pole to the South Pole. These vertical strips are then fitted with their own individual coordinate system to improve accuracy and minimize distortion (though it t's nowhere near perfect.) UTM is always in meters.
Spatial auto-correlation (spatial dependency) as an issue associated with representing GI
Toiler's first Law of Geography -Everything is related to everything else, but near things are related more than distant things. -*Opportunity* provide by Spatial auto-correlation --Spatial sampling and Interpolation {Since "near things are related', maybe it is unnecessary to collect GI at every location} -*The Violation* of Spatial auto-correlation ***Basically have spread out samples so that you get a good representation of an area***
Measuring/Recording Topology (Basic Elements?)
Topology in GIS is generally defined as the spatial relationships between adjacent or neighboring features Basic elements: -Point (0 dimension) -Line/Arc (1 dimension) -Polygon (2 dimension)
Re-Projecting
Transformation between Projected Coordinate Systems 1. Transform PCS 1 BACK to Datum 1 Lat&Long 2. Transform Datum 1 to Datum 2 3. RE-project Datum2 using the new map projection
Calculation of standard UTM Zone number for a location
UTM Zone=Ceiling[(180+longitude)/6] Ceiling (x): rounding x up. NOTE: Use negative numbers for western hemisphere longs, and positive for eastern longs
When do we use Affine Transformation for coordinate system transformation?
Uhh
Location description in GIS:
Unique Universal Constant over time Numerical -Ask if methods of describing location fit into these categories to figure out which is most useful (Methods: Lat&Long, Zip codes, Place names)
From-To Run Length Encoding
Value (theme; A,B,C...) ; From (coordinates of first block of theme) ; To (coordinates of last block of theme)
Value Point Run-Length Encoding
Value (theme; A,B,C...) ; Point (which pixel the last block of that theme section ends at, when reading left to right row by row, top row to bottom row)
Standard Run-Length Encoding (raster)
Value (theme; A,B,C...) ; Run-Length (How many squares in a row are the same theme) ; Row (which row it is in)
Some Projected coordinate systems
Wisconsin state plane, UTM, etc
How does a raster data model represent spatial data? How does it represent a point feature, a linear feature, and an area feature?
With pixels. The pixels vary by color and represent land theme fields. A point feature is represented by one pixel (a different color than the pixels surrounding it), a linear feature, like a river, would be pixels in a line, and an area would be a field of continuous pixels.
Local Datum
a datum that finds a best-fit for a particular region; such datums are frequently poorer fits outside their intended regions of use and should not be used for regions other than those for which they were designed
Arc (Link/Edge)
a directional line (starting & ending nodes specifies)
Node
a point at the intersection of two or more lines (or "meaningful" point feature
Ground surveying
accurately determining the terrestrial or 3D position of points and the distances and angles between them
Time (as an attribute) can sometimes:
add another dimension to a map in GIS
Polygon
an area enclosed by a set of arcs
Satellite Remote Sensing
capture geographic info using electromagnetic sensors
You can join tables together through _____________
common fields
Byte
consists of 8 bits, the basic unit of storage in a computer
Polyline
consists of more than one line segment
Bit
one square unit stating on/off
Vertex/Shape Point
points that are linked to form lines
Satellite data
the main idea behind remote sensing is the storing of reflected electromagnetic energy by a sensor that is distant from the object being sensed
US Public Land Survey System (PLSS)
the primary way that land is subdivided in the US by using a grid system based on the 4 cardinal directions -'Section' is the formal smallest subdivision in PLSS
13:
there are 0 nodes because they aren't intersecting each other, just overlapping.
To georef an image into a local coordinate system (practice exam)
you never georef to a local coordinate system TO a projected coordinate system? You never project to a projected CS OR a Local coordinate system
Disadvantages of a Raster Model
• Large data volumes • Object shapes cannot be precisely represented when pixel size is large • Location is not precise • Topology cannot be explicitly coded • Coordinate transformation often results in loss of information
Advantages of a Raster Model
• Simple data structures (matrix) • Mathematical computation and spatial overlay among multiple raster layers are easy because all data layers consist of pixels (simple and regular shape) • Ability to accommodate spatial variation through decreasing pixel size