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Welcome to the web tutorial about creating a thematic join. In MapInfo Professional, you can
use a thematic map to shade one table with data from another as along as there is some common
element between them. That common element is used to tell MapInfo Professional how to join
the two tables together.
In this example, you are going to shade the States map with information from the Sales
table.
Both tables have a State abbreviation column that will serve as the common column
between the two tables.
The columns don’t need to be named the same, they just have to have the same information.
Notice that there are only 42 records in the Sales table. That means that not all of the
States will be shaded since that table has 51 records.
To create the thematic map, go to the Map menu and choose Create Thematic Map. Select
Ranges as the type and then the template that you wish and click next. The table that you are
going to shade is still the States table but since the field is actually coming from another
table, you will have to choose Join. When you choose Join, it automatically opens up the
Update Column for Thematic dialog box. This is where you specify which column and table
to use for your shading and how the tables should be joined together. First choose the
appropriate table – it will be Sales_03. Then choose what to calculate from which column.
You can choose sum, minimum, maximum and others. This example is a one to one
relationship, that is one state has one sales amount, so you will use value. Then choose the
column you wish to calculate the value. For this example, it will be Total Sales.
Finally, you will need to specify how the tables are being joined together. Remember
earlier that the two tables share a State abbreviation column. Click Join and pick
both columns. MapInfo Professional will try to pick the columns for you, but it
doesn’t always pick the right ones, so it is always a good idea to at least check. You can
click OK to go back to the step 2 dialog box. Remember that some of the rows will not
match because there are only 42 in the Sales table. That means that those that do not match
will have a value of zero which you can choose to ignore.
In step three, you can customize the styles and legend if you wish or just click okay to see
your map.