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Lecture-7_Bb_1SlidePerPage - Spatial Analysis II Spatial...

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Unformatted text preview: Spatial Analysis II Spatial Analysis II Transformations (1 of 2) Transformations Trans ________ Datasets Create new objects and attributes, based on simple ________ or complex ________ • involving geometric construction or calculation • may also create new attribute fields, calculated from existing fields or automatically derived from operations Note: vector to raster (Spatial Analyst/Convert/Features to Raster) Transformations Trans Simple Recoding Recoding is needed sometimes to ________ from lower level spatial units or detailed classes into higher level unit or classes, or from one classification into another • e.g. classify population density from #/Square Miles to low, middle, high Vector data: • usually requires adding a new attribute (field); assign values to the new field based on one or more existing attributes; after recoding, some previous boundaries tt need to be removed Raster data: • using special recoding tools Recode Vector Data Add a new field in ArcMap 2 3 1 Select/Calculate 1 3 2 Dissolve: features (remove the boundaries) with the same same for specified attribute(s) for specified attribute(s) Recode Raster Data 1 ArcMap, Spatial Analyst Extension 2 2 3 Classification… Bu Buffering (Dilation) Create a new polygon object consisting of areas within user defined of areas within a user-defined _______ of an existing object. The application areas are enormous • e.g. to determine areas impacted by a proposed highway to determine areas impacted by proposed highway • e.g. to determine the service area of a proposed hospital Feasible in either _____ or _____ mode The distance is mainly based on __________ distance However, you may use other distances, like However, you may use other distances, like travel _____, travel _____. But these later distances may not be supported by vector tools or users may have supported by vector tools or users may have to use network analysis. Discrete Buffering For Vector Data Point Polyline Polygon The buffer distance is discrete, no difference will be made between locations within a buffer ill Can be _____ or _______ polygon boundary… Can be _____ or _______ polygon boundary… You can create buffers with several ________… Buffer: Creates new buffer polygons around specified Input features (polygons, lines, points). features (polygons, lines, points). Dissolve Type: None Dissolve Type: All Dissolve Type: All Continuous Distance Surface To further differentiate the distance of locations to certain sources In ArcMap OR ArcToolBox OR • In ArcToolBox • In ArcMap, Spatial Analyst, Distance/Straight Line… Outputs The value of each cell shows which of the 3 points (identified value of each cell shows which of the points (identified by ID here) is closest to the cell The value of each cell shows the direction from each cell to its closest point of the 3 Input The value of each cell shows the distance from the cell to the its closest point of the 3 Buffering For Raster Data Bu Result: Straight Line Distance grid: cell Line Distance grid: cell containing the to the nearest feature for that cell. 16 distance to the nearest town • e.g. distance to the nearest town Straight Line Allocation grid: cell value identifying which it is close to it is close to • e.g. which town is the nearest from the cell Straight Line Direction grid: Line Direction grid Cell value is the direction from the cell to the nearest _______ • 0-north • e.g. direction from a cell to the nearest town Cost Weighted Continuous Distance Surface Cost Used when travel cost is different at different places, e.g. travel across dense forest is higher than along road e.g. travel across dense forest is higher than along road A grid grid (or cost grid) can be added to specify difficulty when traveling across a location (cell). The cost grid could be based on set of criteria The cost grid could be based on a set of criteria Cost weighted distance grids better depict . City limits Areas reachable in 5 minutes Areas reachable in 10 minutes 10 minutes Other areas Continuous Distance Surface To further differentiate the distance of locations to certain sources In ArcMap OR ArcToolBox OR A cost weighted distance example Combine Combine Maps: Map Overlay To incorporate different information based on common location common location Map Map Overlay is a key concept in GIS. Many types of map overlay are possible some are implemented in GIS polygon/ Only some are implemented in GIS, polygon/ polygon overlay is the most commonly used Points Points Lines Polygons Surface Lines Polygons Surface Point/Polygon Overlay Determines whether a single/many point(s) is contained by one or more polygons e.g. used to assign crimes to police precincts, used to assign crimes to police precincts disease cases to census tracts, accidents to reporting counties Or to find what kind of land use type each of the random points falls in Implementation is based upon a point in polygon algorithm polygon attributes may be added to point attribute table or vice versa Point/Pol Point/Polygon Overlay The Point in Polygon Algorithm Draw a line from the point to infinity in li th any direction, and count the number of intersections between this line and each polygon’s boundary. The polygon(s) with an number of an number of intersections is the containing polygon All other polygons have an number of intersections. number of intersections. Polygon Overlay Two Cases: di For discrete objects (polygons w/ For fields (polygons w/ the spatial extent) and spatial extent) Discrete object case: Find the pol Find the polygons formed by the fo the intersection of two polygons. Many related questions can be answered, e.g. • Do two polygons intersect? (Do service areas of a hospital/store/fire station overlap with those of another?) th • Where are areas in Polygon A but not in Polygon B? Polygon Overlay, Discrete Object Case B A 1 2 3 4 7 6 8 5 9 In this example, two polygons are intersected to form 9 new polygons new polygons. One is formed from both input polygons; Four are formed by Polygon A and not Polygon B; and Polygon B; and Four are formed by Polygon B and not Polygon A. Polygon Overlay, Discrete Object Case A B 1 2 3 4 7 6 8 5 9 OID Att. Of Poly. A 1 A OID Att. Of Poly. B 1 B OID FID_PolyA FID_PolyB Att. Of Poly. A 1 1 ‐1 A 2 ‐1 1 <Null> 3 1 ‐1 A 4 ‐1 1 <Null> 5 ‐1 1 <Null> 6 1 1 A 7 1 ‐1 A 8 ‐1 1 <Null> 9 1 ‐1 A Att. Of Poly. B <Null> B <Null> B B B <Null> B <Null> Polygon Overlay, Field Case Two complete layers of polygons are input, representing two classifications or representing two classifications or ________ kinds of ________ (attributes) of the ______ ________ (same spatial extent) e.g. soil type and land ownership soil type and land ownership The layers are overlaid, and all intersections are computed, creating a new layer, which has information (attributes) from information (attributes) from ________ layers layers (the (the attributes are said to be ____________) e.g. each polygon in the new layer has both a soil type and land ownership type and a land ownership Polygon overlay is central to the use of GIS in Spatial Decision Support system, When a number of criteria have to be balanced in some way to achieve a desired outcome Polygon Overlay, Field Case Pol A layer representing a field of land ownership (colors) is overlaid upon layer of soil type (colors) is overlaid upon a layer of soil type (soil (soil types A, B). The result after overlay will be a single layer with 5 polygons, each with a land ownership value and a soil type. Owner X Owner Y Public A B •Overlay Tools • between point/line/polygon with polygon • between polygons only Clip (The Cookie Cutter) Uses the outer boundary of a polygon feature class/coverage (The Clip Feature) to (cookie) cut the features out of an the features out of an input feature class/coverage Split p, Like clip, but it cuts from the input several outputs based on one attribute of the split input input Erase NOT operation of clip, inverse of the clip result Symmetrical Difference Features or portions of features in the input th and update features which do not overlap will be written to the Output Feature Class ...
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This note was uploaded on 09/21/2011 for the course GIS 4043C taught by Professor Roberts during the Spring '11 term at FAU.

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