Working with Vector Data - Desktop GIS: Mapping the Planet with Open Source Tools - page 39

Figure 3.9: QGIS continuous color renderer settings
Now that we are proficient in adding a layer and adjusting its appear-
ance, let's take a look at Harrison's bird data.
Viewing the Bird Data
To answer all of Harrison's questions about his data, we'll use QGIS's
Continuous Color, Graduated Symbol, and Unique Value renderers.
Using Continuous Colors
In continuous color rendering, you set a color for the minimum and
maximum values in your data, and it automatically assigns colors to
each feature. It turns out this is a quick way to render Harrison's bird
sightings to get a feel for the relative distribution of birds. The vector
Layer Properties dialog box with the continuous color option selected is
shown in Figure 3.9 .
To set up the renderer, we selected a start and end (minimum and
maximum) color. You could use any colors, but we chose a blue to red
transition, going from dark blue to dark red. You could just as easily
go from an orange to a dark green. The number of birds per site are
represented from the fewest (dark blue) to a moderate number (purple)
to the most (dark red). The count field from the attribute table contains
the number of birds per site and is used to classify the data.