Page History

...

1. In the Contents pane, right-click the HGAC_tracts layer name and select Attribute Table.
   
   A table view now appears docked beneath your map view. Each row, or record, in your table corresponds to exactly one census_tract polygon on the map. Each column, or field, in your table represents a variable describing the census tracts.
   
   Every geodatabase feature class has two to four default fields, which cannot be edited or deleted. The leftmost OBJECTID field is a unique ID that is automatically numbered from 1 to the total number of features at the time of creation. The Shape field indicates whether the feature geometry contains points, lines, or polygons.
   
   
2. In the table view, use the scroll bar at the bottom to scroll to the far right of the table.
   
   The other two default fields are the last Shape_Length and Shape_Area fields which contain the perimeter and area of the census tracts, respectively. A line feature class will only contain the Shape_Length field and a point feature class will not contain either field. The units of these fields correspond to the units of the projection in which the data coordinates are stored.
   
   
3. In the Contents pane on the left, double-click the HGAC_tracts layer name.
4. In the 'Layer Properties' window, in the left column, click the third Source tab.
5. Scroll to the bottom of the window and click to expand the Spatial Reference section.
6. Use the scroll bar on the right to scroll through the metadata.
   
   Within the Spatial Reference section, notice that the projected coordinates system is NAD 1983 StatePlane Texas S Central and the linear unit is US Survey Feet. Therefore, the Shape_Length field is displaying feet and the Shape_Area field is displaying square feet. Before measuring distance or area. More information about projections is available in the Introduction to Coordinate Systems and Projections tutorial.
   
   The majority of the remaining fields contain 2010 census data that was aggregated to the census tract level by the Census Bureau.
   While the fields have cryptic names, they are explained in the Field_Names.xls file that came with the original census data download from the H-GAC Regional Data Hub. For this tutorial, we will be interested in field H_1 (Housing Units–All) and H_3 (Housing Units--Vacant).
   
   
7. Scroll back to the far left of the table.
8. Double-click the 'Name10' field header to sort the census tracts numerically.Scroll back 
9. Double-click the  the 'NameName10' field header a second time to sort the neighborhoods alphabeticallyin descending order.
10. To select a neighborhood census tract from the table, click the gray square to the far left of each row.
11. To select an adjacent section of records, hold down Shift and select a record below or above the currently selected record to automatically select all records in between.
12. To add or remove individual records from the selection, hold down Ctrl and select another record.
    
    Notice in the bottom left corner of the Census_2010_By_SuperNeighborhood HGAC attribute table, it indicates the number out of 88 1,109 table records (and corresponding map features) that are currently selected.
    Image Removed
    Image Added
    
    The two buttons to the left allow you to toggle between 'Show all records' and 'Show selected records'.
    
    
    
    Note that if 'Show selected records' is active and no records are currently selected, the table view will appear empty. Toggle If necessary, toggle back to 'Show all records' to view the table.
    
    
13. At the top of the Census_2010_By_SuperNeighbrhood table view HGAC_tracts view, click the Clear button.
    
    Image AddedImage Removed
    
    
14. Close the attribute table.
    Image Removed
    Image Added

Symbolizing Layers By Attributes

...

1. In the Contents pane, right-click the Census_2010_By_SuperNeighborhood HGAC_tracts layer name and select Symbology.
2. Use the primary 'Symbology' drop-down menu to select Graduated Colors.
   
   
   
   
3. Use the 'Field' drop-down menu to scroll down sixth from the bottom and select the SUM_Vacant field. This field stores the number of vacant housing units within each neighborhood.
   
   The map view now displays a choropleth map, where the darker colors represent higher numbers of vacant housing units. 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 symbology. Now you will try normalizing by the area of the neighborhood.
   
   
4. 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 course, 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 field is displaying square decimal degrees and the map is displaying number of vacant housing units per square decimal degree. This is a somewhat incomprehensible 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. Notice that according to the density of vacant housing units, the greatest amount of vacant housing units appear to be both inside and outside the loop along 59.
   
   
5. Use the 'Normalization' drop-down menu to select the SUM_HU100 field.
   
   The map is now displaying the number of vacant housing units divided by the total number of housing units, or the percent vacant housing units. While both methods of symbolizing the vacant housing units are technically correct, this is probably the most common method.
   
   
6. On the lower half of the Symbology pane, click the Histogram tab.
   
   
   
7. Use the 'Method" drop-down menu to select Equal Interval.
   
   Notice how the map changes. Equal Interval divides the range of attribute values into equal-sized subranges.
   
   
8. Use the 'Method" drop-down menu to select Quantile.
   
   Again, the display of data on the map changes. Quantile assigns the same number of data values to each class.
   
   
9. Use the 'Classes' drop-down menu to select 20.
10. Use the 'Classes' drop-down menu to select 4.
    
    Observe how changing the number of classes alters the display. 
    
    
11. Use the 'Color Scheme' drop-down menu to select a different color scheme of your choice.

...

1. Use the primary 'Symbology' drop-down menu to select Unique Values.
2. Use the 'Field 1' drop-down menu to select Name.
3. In the Contents pane, collapse the Census_2010_By_Superneighborhood HGAC_tracts symbology.

Selecting Features Programatically

...