Ana -

There are a few different ways you could do this.  Start with your data
in three columns.  Leave Cell A1 blank, type ATMs in B1, and type
Brazilians in C1.  List your cities below A1, and in the same row as the
city, list the number of ATMs and of Brazilians.  Like this, only with
real numbers:

             ATMs    Brazilians
Brasilia     1500      2000000
Rio          2100      1250000
Sao Paolo    1250      1750000

Select the range of data (including the top row), start the chart
wizard, and on step 1, you might want a chart type like Lines On Two
Axes, on the Custom tab.  This puts the ATM number on the left hand
axis, and the population on the right.  If you make a line chart on just
one axis, you can move a series to the second axis by double clicking it
and selecting Secondary on the Axis tab.

Another way to show this would be to select just the data in columns B
and C, and make a Scatter chart.  This shows how the number of ATMs
varies with population.  If you know ahead of time that you want
population on the X axis, switch columns B and C in the data before
making the chart.  If you want to switch X and Y after making the chart,
right click the chart, choose Source Data from the pop up menu, click on
the Series tab, select the series, and switch what's in the Y Values and
X Values boxes (copy-paste or selecting with the mouse).

A scatter chart shows part of the picture, but it's even better if you
label the points, to know which city corresponds to which point.  You
can do this manually, and you'll become easily bored.  Fortunately,
there are a couple useful and free Excel addins that can automatically
label data points, using labels in a worksheet range:
    Rob Bovey's Chart Labeler, http://appspro.com
    John Walkenbach's Chart Tools, http://j-walk.com
Download and install one of these, and use it to apply the city names in
column A to the points in the chart.

- Jon
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Jon Peltier, Microsoft Excel MVP
http://www.geocities.com/jonpeltier/Excel/index.html
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