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Symbolizing Layers By Quantity

1. In the Catalog pane, add the US_tract_2010_harriscounty feature class to the Houston History Map view. 
2. In the Contents pane, right-click the CensusUS_tract_2010_By_SuperNeighborhood layer harriscounty layer name and select Symbology.
3. Use the primary 'Symbology' drop-down menu to select Graduated Colors.
4. Use the 'Field' drop-down menu to scroll down sixth from the bottom and select the SUM_Vacant AV0AA2000 field. This field stores the total number of vacant housing units within each neighborhoodpersons per census tract in the year 2000.

The map view now displays a choropleth map, where the darker colors represent higher numbers of vacant housing unitspeople. In studying the map, it appears as if the most vacant housing is in southwest Houston outside the Loop. While this is true according to raw counts per neighborhood, there could be differences in the neighborhoods that are unaccounted for in this symbologythere does not appear to be a pattern. Now you will try normalizing by the area of the neighborhoodcensus tract.

1. Use the 'Normalization' drop-down menu to scroll to the bottom and select the last Shape_Area field.

As discussed in the Introduction to GIS Data Management coursementioned previously, the projection of the census layer is WGS 1984. Therefore, the layer is unprojected and the coordinates are stored in angular units of decimal degrees. Therefore, the Shape_area Area field is displaying square decimal degrees and the map is displaying number of vacant housing units people per square decimal degree. This is a somewhat incomprehesible unit, however, the values are still proportional to how they would be in a different unit and the relative coloring on the map remains correct. If you wanted to make a map that displays vacant housing units per square mile, then you would add a new field need to the attribute table and use the calculate projecting project the US_tract_2010_harriscounty layer. Projecting is further covered in the Introduction to Coordinate Systems and Projections course.

Notice that according to the density of vacant housing unitspopulation count, the greatest amount of vacant housing units people appear to be both inside and outside the loop along 59.

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