Analysis of GIS Data by Simple Examination - Introducing Geographic Information Systems with ArcGIS - page 373

40. Experiment with other layer properties and data frame properties. These windows allow you a
great deal of control over what is displayed. You should become familiar with them. A large part
of successfully operating ArcMap is knowing where to find and use the various controls.
41. Right-click the Landcover layer and remove it from the map. Remove Roads as well. Make sure
Soils is turned on. The map now appears consisting of a homogeneous color background with
lines dividing polygons of Soils.
As before, you could identify individual polygons with the Identify tool. You could place text in each
polygon with the labeling facility. You could open the attribute table and, by selecting polygons, see the
corresponding rows in the table, and vice versa. All of these techniques are useful, but none gives you a
very good picture of what features are where, and it doesn't let you compare various features. In the steps
that follow, you change this by presenting the polygons as a thematic map, with different colors for each
type of soil. First you label the polygons with SOIL-CODE.
42. Bring up the layer's properties window. (What are two ways to do this? ____________________,
____________________.) Click the Labels tab. Check the box that says Label features in
this layer. Use SOIL-CODE in the Label field. Click Apply and on OK. Check out the resulting
display.
43. Bring up the layer's properties window again. Click the Symbology tab. In the Show box you will
probably see Single Symbol highlighted under Features. Click Categories and make sure Unique
values is selected. Make the Value Field SOIL-CODE. Click Add All Values. Click Apply, then OK.
Notice that all polygons labeled Sg are the same color. Change the symbol used to depict the
water to Atlantic Blue or Pacific Blue. If there are other polygons with a color close to the blue
you picked, change them to some other color.
44. Now you can clearly get an impression of the locations and amounts of the various soil types.
What (commonly named) color is associated with Ko? ________________
45. Change the labeling so that soil suitability (SUIT) is shown. By inspecting the map and the
legend, and using the Identify tool if necessary, determine the soil codes of the soils that have
suitability 1. ______________________________.
Suitability 2? ______________________________.
Suitability 3? ______________________________.
What is the suitability value shown for water? _________.
46. Now switch the labeling and the color representation, that is, label the polygons again with the
soil code and show the suitability with different colors. Check your answers from the
last step.
47. There are practical and visual limits to the numbers of color categories you can add to a map.
So ArcGIS has the capability to display only the categories you choose. To see how this works,
under Symbology in the Layer Properties window, click Remove All, then click Add Values. Now
you have the option of adding only some of the values. Since soils suitable for the Wildcat Boat
facility are only 2 and 3, add only those values (use Ctrl-click). Click OK, Apply, then OK. Note
that the rest of the map is colored with the <all other values> symbol.