Database Reference
In-Depth Information
Circle Maps
So far, we've created a number of charts and graphs of various places (chiefly New York
City), but we have yet to create a map. At its simplest, a map shows a graphical depiction of
some place, with markings for objects in that place. The markings on the map, like roads,
borders, or bridges, are spaced in proportion to their spacing in the real world.
A map, then, becomes an ideal chart on which to visualize data. One way to visualize data on
a map is to place a circle at a particular location, the size or color of which is proportional to
some quantity associated with that location. This type of map is sometimes called a “bubble
map.”
NOTE
Why use a circle? Because we quickly identify a circle with its center point; there are no
corners that would suggest another intended location.
There are plenty of ways to make these types of maps, including using the D3.js library or
the Processing environment. Tableau provides an incredibly easy way to create a circle map
using the same drag-and-drop interface we've been exploring. Let's try it out.
If we go back to the New York City boroughs population data we considered in
Chapter 2
,
we can see that creating a map with circles is easy. There are three ways to do it:
1. Double-click on any geographic data field (one that has a globe icon next to it).
2. Select the geographic field by clicking on it, open the Show Me panel, and select
sym-
bol maps
.
3. Drag
Latitude (generated)
to the Rows shelf, drag
Longitude (generated)
to
the Columns shelf, and then drag
County
to Detail.
All three of these methods result in the view shown in
Figure 10-2
, in which Tableau places a
blue circle at the center point of the coordinates of the geographic field.
