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38 Cards in this Set
- Front
- Back
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What is overlay?
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- multiple layers of features on top of one another
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What is buffering?
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- a spatial retrieval around points, lines or areas based on distance
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What are the three main types of overlay operations? What do overlays do?
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1. Union
2. Intersect 3. Identity - computer the geometric intersection of 2 polygon coverages |
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What is Union overlay? Draw and give example.
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- all polygons from both coverages will be split at their intersections and preserved in the output coverage
- both union and input are combined and everything is preserved in the output coverage - Ex. within 25 miles of a city OR within 25 miles of a major river |
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What is Intersect overlay? Draw and give example.
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- only those features in the area common to both coverages will be preserved in the output coverage
- Ex. within 25 miles of a city AND within 25 miles of a major river |
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What is Identity overlay? Draw and give example.
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- all features of the input coverage as well as those features of the identity coverage that overlap the input coverage are preserved in the output coverage.
- Ex.portion of the major city buffer WITHIN the major river buffer |
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How does identity analysis work?
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- discovers geometric relationships (overlap) between the input features and the identity features
- cracks (inserts vertices at the intersection of feature edges) and clusters (snaps together vertices) the features - determines the spatial reference for processing (output spatial reference), all the input feature classes are projected into this spatial reference |
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What does the Erase tool do? Draw.
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- this tool creates a feature class from those features or portions of features outside the erase feature class.
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What does the Symmetrical Difference tool do? Draw.
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- this tool creates a feature class from those features or potions of features that are not common to any of the other inputs
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What does the Update tool do? Draw.
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- this tool updates the attributes and geometry of an input feature class or layer by the update feature class or layer that they overlap
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What two overlay methods do Point in Polygon and Line in Polygon use?
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Union and Intersect
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What are the four types of Extract Tools?
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1. Clip
2. Select 3. Split 4. Table Select |
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What is Clip? Draw.
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- extracts a section of from an input feature class that overlaps with the clip feature class
- the clip tool is similar to the intersect tool, however, the clip tool does not transfer any attributes from from the clip feature class to the output |
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What is Select? Provide example.
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- extracts features from an input feature class or layer and stores them in a new output feature class
ex. picking out Garry Oak ecosystems in BC - can make selections based on attribute data in a table |
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What is Split? Draw.
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- the spatial extraction of features by clipping portions of the input feature class into multiple feature classes.
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What is Table Select?
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- extracts selected attributes from an input table based on attribute query and stores them in an output table.
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What are the four Proximity Tools?
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1. Buffer
2. Multiple Ring Buffer 3. Near 4. Point Distance |
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What is a buffer?
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- the construction of area features by extending outward from point, line or polygon features over a specified distance
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What is Multiple Ring Buffer? Draw.
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- creates a new feature class of buffer features using a set of buffer distances
- can have two buffers of two different aspects of a project |
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What is Near?
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- computes the distance from each point in a feature class to the nearest line or point in another feature class
- uses Pythagorum theorem |
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What is Point Distance?
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- computes the distances between point features in one feature class to all points in a second feature class that are within a specified radius
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What is Geocoding?
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- creates spatial data from information that describes or names a location (ex. address)
- GIS assigns coordinates to data records - ex. making map of postal codes |
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What is Frequency?
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- produces a list of the unique code occurrences and their frequency in an output table for a specified set of fields from an input feature class or table
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What are Summary Statistics?
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- statistics about fields from an input table or feature class that are then saved as an output table
- include: sum, mean, minimum, maximum, standard deviation, etc |
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What are Local Functions?
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- compute an output raster data set where the output value at each location is a function of the value associated with that location on one or more raster datasets
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What are Focal Functions?
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- produce an output raster dataset in which the output value at each location is a function of the value at a location and the values of cells in a specified neighborhood around that location
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What are Zonal Functions?
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- compute an output raster dataset where the output value for each location depends on the value of the cell at that location and the association that that location has within a cartographic zone
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What are Global Functions?
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- compute an output raster dataset in which the output value at each cell location is potentially a function of all the cells in the input raster data sets.
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What does XOR do in a raster calculator?
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- compares 2 input bits and generates 1 output bit. If the bits are the same the result is 0. If they are different the result is 1.
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What is Overlay Using Maximum?
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- when overlaying 2 raster images the output product chooses the highest value for each pixel of the 2 input layers
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What is Recode?
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- changes certain input values to different output values. Ex. yellow and green become black, red and orange pixels become white.
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What are the seven types of Terrain Analysis?
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1. Contours
2. Slope 3. Aspect 4. Hillshade 5. Viewshed 6. Cut/Fill 7. Hydrologic Features |
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What are contours?
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- polylines that connect points of equal value such as elevation, temperature, precipitation, pollution or atmospheric pressure
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What is aspect?
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- measured clockwise in degrees from 0 (due North) to 360.
- the value of each cell in an aspect dataset indicates the direction the cell's slope faces. Flat slopes have no direction and are given a value of -1. |
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What is hillshade?
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- setting a hypothetical light source and calculating the illumination values for each cell in relation to neighboring cells It can greatly enhance the visualization of a surface for analysis or graphical display.
- relies on azimuth and altitude of the sun |
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What is Viewshed?
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- identifies the cells in an input raster that can be seen from one or more observation points or lines
- useful for finding the visibility. ex. finding a well-exposed place for communication towers |
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What is Cut/Fill?
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- summarizes the areas and volumes of change between 2 surfaces
- by taking 2 surface rasters of a given area from 2 different time periods, the cut/fill function will produce a raster displaying regions of surface material addition/removal - negative values indicate areas that have been filled, positive values indicate areas that have been cut - ex. used to track erosion in a river valley |
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What is Reclassification?
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- reclassifying data means replacing input cell values with new output cell values (for raster data)
- can be used to group certain values together or to replace values based on new information, etc |
