Buffers, cost surfaces, least cost path
+Resources: +ESRI virtual campus + +
+Include resulting maps into your report +(use your judgment to decide which results to include). Adjust the colors and symbology of displayed layers to match the cartographic standards (lakes are displayed in blue etc.) + + + +
+Create the workspace for the current assignment as the folder Buffers_cost
+
+To constrain analyses in a similar manner as g.region,
+set the spatial extent using the options under Environments, for example:
+to constrain analyses results to the extents defined by intersection of input features:
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+Start ArcMap. +From the menu Geoprocessing -> Environments... -> Processing extent. +Choose Intersection of Inputs from the drop down menu. +Click 'OK' ++ +
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+To work on a subset, clip your data to a given spatial extent.
+Constrain the drawing of project layers to a user specified extent.
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+Start -> Programs -> ArcMap +Add ./ncrast.mdb/elev +Add ./ncshape.mdb/streets_wake +Dbl. Click the 'elev' layer in the TOC +Go to -> Layer Properties -> Extent +Write down the four numbers in the text fields labeled: 'Left', 'Right', 'Top', 'Bottom' +Click 'OK' +Dbl. Click 'Layers' in the TOC +Go to ->'Data Frame Properties' -> 'Data Frame' -> 'Clip Options' -> 'Clip to Shape' +Click 'Specify Shape' +Select 'Custom Extent' +Uncheck the 'Degrees' check box +Enter the four numbers you recorded earlier in their appropriate text fields +Click 'OK' +Click 'OK' ++ +
Find developed areas close to lakes
+Create the buffers: + ++File -> Add Data -> Add Data... +Select ./ncrast.mdb/lakes +Select ./ncrast.mdb/landcl96 +Check out a Spatial Analyst Extension license (Menu -> Customize -> Extensions -> Spatial Analyst box needs to be checked) +Open the ArcToolbox (you may already have it open) +Select 'Spatial Analyst Tools->Distance->Euclidean Distance' +Set 'Input raster' to 'lakes' +Set Output distance raster' to '\Buffers_cost\lk_dist' +Set 'Maximum distance' to '500' +Leave the rest as defaults +Click 'OK' ++ +
+Select the locations that overlay developed areas: + +
+Select 'Spatial Analyst Tools->Map Algebra->Raster Calculator' +Type in the expression: SetNull( "landcl96" > 2, "lk_dist") +Set the Output raster to './Buffers_cost/dev_lakes +Click 'OK' ++ +
Compute cost surface from accident based on speed limits
+ ++File -> Add Data -> Add Data... +Select ncshape.mdb/streets_wake +Open the ArcToolbox (if not already open) +Select 'Conversion Tools->To Raster->Polyline to Raster' +Set 'Input Features' to 'streets_wake' +Set 'Value field' to 'SPEED' +Set 'Output Raster Dataset to './Buffers_cost/str_speed' +Set Cellsize to 30 +Leave the others as defaults +Click 'OK' + +File -> Add Data -> Add Data... +select ./ncshape.mdb/fire_pt ++ +
+Set the working directory: + +
+Select Geoprocessing -> Environments... +Under 'Workspace' set the 'Current Workspace' to '.\Buffers_cost' +Under 'Raster Analysis' set the 'Cell Size' to 'Same as layer str_speed' +Under 'Raster Analysis' set the 'Mask' to '.\ncshape.mdb\boundary_wake' +Click 'OK' ++ +
+Assign travel time per cell in hours, compute cost surface.
+Assign null values a speed of 5.
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+Open the ArcToolbox (if not already open) +Select 'Spatial Analyst Tools->Map Algebra->Raster Calculator' +Type in the expression: Con(IsNull("str_speed"),5,"str_speed") +Set the Output raster to 'str_speed2' +Click 'OK' ++ +
+Calculate the travel time and cost surface. +
+In ArcGIS cost is defined per map unit (meters in this case). +We create a cost raster where cost is time to cross one map unit. +Where does the 0.00062137 constant come from? + +
+Select 'Spatial Analyst Tools->Map Algebra->Raster Calculator' +Type in the expression: 0.00062137 / "str_speed2" +Set the 'Output raster' to str_trv + +Open the ArcToolbox (if not already open) +Select 'Spatial Analyst Tools->Distance->Cost Distance' +Set 'Input raster or feature source data' to 'fire_pt' +Set 'Input Cost raster' to 'str_trv' +Set 'Output distance raster' to './Buffers_cost/str_cost' +Set 'Output backlink raster (optional)' to './Buffers_cost/backlink' +Leave the rest as defaults +Click 'OK' ++ +
Find cost from selected firestations
+ ++File -> Add Data -> Add Data... +Select ./ncshape.mdb/firestations +Open the ArcToolbox (if not already open) +Select 'Spatial Analyst Tools->Extraction->Sample' +Set 'Input rasters' to 'str_cost' +Set 'Input Location raster or point features' to 'firestations' +Set 'Output table' to './Buffers_cost/station_costs' +Leave everything else as defaults +Click 'OK' ++ +
+Add the table of costs (NOTE: in Arc 10 this should be added automatically at the bottom of the TOC). +However, if the table does not get added: +
+ +File -> Add Data -> +Select '.\Buffers_cost\station_costs' ++ +
+Open the station_costs table and sort on the field 'STR_COST': + +
+right click 'station_costs' -> Open +right click column named 'STR_COST' and choose 'Sort Ascending' +Note the range of cost values. +Close the table ++ + + + +
+Find shortest path from nearby firestations.
+Note: create the firestations as a shapefile if the below
+does not work with geodatabase firestations.
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+
+Open the ArcToolbox (if not already open) +Select 'Spatial Analyst Tools->Distance->Cost Path' +Set 'Input raster or feature destination data' to 'firestations' +Set 'Destination field' to 'OBJECTID' +Set the 'Input cost distance raster' to 'str_cost' +Set the 'Input cost backlink raster' to 'backlink' +Set the 'Output raster' to '.\Buffers_cost\cost_path' +Set the 'Path type' to 'BEST_SINGLE' +Click 'OK' ++
+Note: to see the resulting least cost (drive-time) path +you may have to turn off some or most of the layers in your TOC. + +