Choropleth maps are very common. Most people have seen them, but few know them by this
name. They are usually referred to as "Thematic Maps". These maps use coloring and/or shading
to depict values of selected characteristics. Choropleth maps are useful when the data is
reported by area, not just by location or point.
Choropleth Maps are very useful for making comparisons or when viewing data in geospatial
relationships that has been transformed into percentages or numbers for given areas.
Dot Density Maps
Dot density maps are sometimes called dot distribution maps because they show where particular
data characteristics occur. Dot density maps use dots or other symbols to represent the
number of occurrences of a given data characteristic in a particular location. Each dot
or symbol used on the map may represent a single entity (one dot = one person) or a group
(one dot = 1000 people).
Dot density maps are most useful for showing where particular data occur. They also enable
area comparisons. Care must be taken when using dot density maps to interpret the "symbol
to data characteristic" ratio. Also, it should be understood that the dots or symbols do
not always indicate the exact location of the data characteristic. Symbols often represent
data occurring within a bounding polygon such as a census tract, zip code or county.
NASA SETI Analytics
Using the location analytics features of
TheTown™ software, the SETI Institute represented personnel at every NASA Astrobiology Site by Zip Code. Clicking
on any symbol to revealed the underlying personnel data.