Scale - Spatial Mathematics: Theory and Practice through Mapping - page 117

Dot density maps offer one way to synthesize information derived from point
sources to suggest information about areas. As we shall see in future chapters,
there are others, as well.
In the next section, you will have the opportunity to put these concepts into
practice. The first activity involves changing the map scale in a web-GIS from
the US Census Bureau. The next activity involves the analysis of population
change using Esri web-GIS tools. In both activities, you will see the effect
that map scale and symbology have on the accurate interpretation of the
data.
5.4 Practice using selected concepts from this chapter
5.4.1 Scale change exercise
Access the TIGERweb mapping service from the US Census Bureau ( http://
tigerweb.geo.census.gov/tigerweb/ ). Consider the sequence of maps shown in
Figures 5.5 through 5.7 and focus on the Lake Michigan coastline that lies
in the state of Illinois as the eastern edge of the greater Chicago metropolitan
area. At a national scale, Figure 5.5 , the coastline appears to be very smooth.
The map shows a representative fraction of 1:18:489, 297 and it displays a bar
scale.
Using the TIGERweb service, zoom in to a level that focuses on the southern
end of Lake Michigan, adjacent to four states: Wisconsin, Illinois, Indiana, and
Michigan ( Figure 5.6 ). The representative fraction of this map is 1:1,155,581.
This fraction is larger than the fraction associated with Figure 5.5 so the map
scale of the map in Figure 5.6 is larger than that in Figure 5.5. Also note
that county boundaries have now entered the picture as a consequence of
Figure 5.5 Representative fraction: 1:18,489,297. Source: US Census Bureau, TIGERweb
(beta), http://tigerweb.geo.census.gov/tigerweb/