Database Reference
In-Depth Information
Visualizing Rates
Now that we have linked these two data sources, our updated Tableau workbook contains
both terms of the refuse per person ratio: the measurement of the amount of refuse in tons
(the numerator) and the count of the number of people in each community district (the de-
nominator). We'll create the rate the same way we created the ratio in the previous section,
but now we need to create a calculated field that includes fields from two different sources,
as shown in
Figure 4-14
.
Figure 4-14. Creating a rate using fields from two data sources
Using the
SUM
aggregation type for both terms in the rate means that we can get meaningful
rates for boroughs as well as community districts. Also, notice we are converting from short
tons (US) to pounds (lbs.) by multiplying the numerator by 2,000—which is how many
pounds are in each ton. On a per person basis, it's much easier for us to think in terms of
pounds, so this is a better unit to use for this comparison.
Now that we have created the rate, we can visualize it. We'll follow the same steps that we
used to create the ratio bar chart in
Figure 4-12
to create the rate comparison bar chart shown
in
Figure 4-15
.
