Database Reference
In-Depth Information
all we know, the districts at the top may be recycling a lot, but they may also be producing a
much higher amount per person. That's where rates come into play.
Rates
Recall that a rate is just a special type of ratio in which the numerator and the denominator
have different units. In the previous example, the ratio of recycle to refuse involved terms
with the same units—namely, tons. When we consider the trash production rate per person,
our numerator is still tons, but now our denominator is the number of people.
But the data set we have been working with so far doesn't include community district popu-
lation. In order to determine trash production per person, we'll need to find a way to include
population data in our analysis.
Going back to the data discovery process in Figure 1-1 , we've gone all the way around the
horse track, and now we have a brand-new question that involves gathering new data.
Ideally, we would find population by community district for September 2011, which is when
the DSNY collection data was taken. We can't find that, but we came come close: 2010
census data puts us within a year's time of the trash collection data, and is probably suitable
to get a reasonable approximation of the trash production rate.
Now that we found population data, how can we create rates with it? Luckily, Tableau allows
us to connect our current workbook to this new data set and “blend” it with the existing data
in the workbook.
Blending Data Sources
From the Data menu of our current workbook, select Connect to Data and then Microsoft
Excel , and browse to the population data file, connecting to the correct sheet in the file and
importing the data as an extract. We now see the new data source appear in the Data area
along with the DSNY data, as shown in Figure 4-13 .
Search WWH ::




Custom Search