Dissolve, Union, Intersect Overlay, Buffer, & Compute
Review Gorr/Kurland, Tutorial 8 (‘Spatial Data Processing’) and Tutorial 9
In ArcCatalog, preview the previously joined tables mdtgr2 (table, geography)
and examine the metadata (especially ‘Spatial Reference Information’).
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.
‘Add Data’: Phurevac, mdtgr2, and mdpopulation.
List Phurevac first in the table of contents, followed by mdtgr2.
Rename Phurevac ‘Evacuation zones’; mdtgr2 ‘Miami-Dade County’;
and mdpopulation ‘Population’.
Create a new group layer.
Display ‘Evacuation zones’ first, then
‘Miami-Dade County’ and ‘Population’.
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).
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).
HURR_CATEG to HURRICANE CATEGORY, and rename the hurricane
category labels in the table of contents: Category 1, Category 3,
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
How can you add a ‘No evacuation’ category that allows
layers to be combined for spatial analysis?
Dissolve and union:
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.
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
all of the features of two layers, ‘Evacuation Zones’ and ‘Miami-Dade County’.
The new layer will be named ‘Miami-Dade, incl. Evacuation Zones’.