assign8 - Assignment 8 Dissolve Union Intersect Overlay...

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1 Assignment 8. Dissolve, Union, Intersect Overlay, Buffer, & Compute Centroids Preliminary § Review Gorr/Kurland, Tutorial 8 (‘Spatial Data Processing’) and Tutorial 9 (‘Spatial Analysis’). § In ArcCatalog, preview the previously joined tables mdtgr2 (table, geography) and examine the metadata (especially ‘Spatial Reference Information’). Then preview Phurevac (hurricane evacuation zones), making sure that its coordinate system matches that of mdtgr2. § In ArcMap, set to store relative path names, set the appropriate coordinate system, and check the display units. I § ‘Add Data’: Phurevac, mdtgr2, and mdpopulation. o List Phurevac first in the table of contents, followed by mdtgr2. Rename Phurevac ‘Evacuation zones’; mdtgr2 ‘Miami-Dade County’; and mdpopulation ‘Population’. o Create a new group layer. Display ‘Evacuation zones’ first, then ‘Miami-Dade County’ and ‘Population’. o In ‘Evacuation zones’, symbolize the value field HURR_CATEG, unchecking ‘All Other Values’ (so that this category does not display in the table of contents). o Adjust the colors of the symbols to reflect the gradation from Category 1 (greatest urgency: need to evacuate for weakest hurricane) to Category 5 (need to evacuate only for strongest hurricane). Rename HURR_CATEG to HURRICANE CATEGORY, and rename the hurricane category labels in the table of contents: Category 1, Category 3, Category 5. Adjust the colors on the Miami-Dade County map. § There is no category for ‘No evacuation’. While this can be easily rectified in terms of mere map display, the problem requires greater work to enable spatial analysis. How can you add a ‘No evacuation’ category that allows layers to be combined for spatial analysis? II § Dissolve and union: o Dissolve aggregates features (i.e. reduces features from more to fewer fields by dissolving the boundaries between adjacent polygons that share the same value for the specified attribute). § A dissolve’s results depend on the particular field(s) selected for the procedure. o Union combines all of the features of two layers. § You can add a ‘No evacuation’ category to the layer discussed above and permit layers to be combined for spatial analysis by using union to combine all of the features of two layers, ‘Evacuation Zones’ and ‘Miami-Dade County’. o The new layer will be named ‘Miami-Dade, incl. Evacuation Zones’.
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2 o This procedure will be easier if we first use dissolve to reduce the number of fields in the layer ‘Evacuation zones’ to only those that we need. o We will use dissolve to extract from ‘Evacuation zones’ the field HURR_CATEG, which will become a new layer to be named ‘Hurricane categories’. We will then union it with Miami-Dade County to make ‘Miami-Dade, incl. Evacuation Zones’. § Dissolve
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This note was uploaded on 07/11/2011 for the course SYA 6356 taught by Professor Staff during the Spring '08 term at University of Florida.

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assign8 - Assignment 8 Dissolve Union Intersect Overlay...

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