Layer Editor -- Section/Interval Settings
Click the Section tab at the top of the form. The Section settings tab panel appears.
Section settings are used to set the intervals for a layer that is to be shown as a thematic map.
A thematic map shows patterns (e.g., solid colors) for geographic objects (e.g., counties) in the map view panel based on the value that a field or attribute takes on based on the query statement in the project file. In the present view (above), the first section (interval) is defined with the query statement:
100*(P070108-p070100)/p070100 < 0
This statement instructs CV to include all counties in this interval if the percent change in total population between 7/1/2000 and 7/1/2008 is less than 0 percent.
Query statements conform to structured query language (SQL) specifications .
To set or modify the name associated with a section/interval, key in the text in the Legend edit box. Note the value in the Legend edit box for interval one is “Lost population" and this is the same text that appears in the legend panel on the main CV screen.
To determine what field names (e.g., p070108) are available and how they are defined requires knowing what attributes have been defined in the shapefile dbf. In this case, the fields in uscty.dbf are defined at http://proximityone.com/cty2008layout.htm.
The thematic map would have a different appearance if the query statement used -5 rather than 0. If the first interval is changed to -5 then the next interval would need to be modified to -5 as well (to insure all counties are accounted for).
This layer presently uses three sections/intervals. While 3 to 5 intervals is good for most applications, some might have fewer and other many more intervals depending on what is required in the map view.
A fourth layer could be added by clicking the plus (+) sign in the visible query listings. The query statement and legend name would then need to be set.
To select a section/interval to change, click on the “visible query” name so that it highlights blue in the lower section of the panel.
To turn off a section/interval, so that it does not appear, remove the check in the Visible check box.
Minimum scale and maximum scale are covered in more advanced sections.