Updating Columns using Thematic Mapping - MapInfo_Pro - 2023

You can use data from another table to construct your thematic map using Update Column. Update Column creates a temporary column in your base table and automatically inserts data into it for your map. This data can be a field taken directly from another table, or aggregated from other data.

For example, you have a table of U.S. state boundaries and a table of U.S. city point locations. Using ranges of values you want to shade the USA table according to the percentage of each state's population living in urban areas. For MapInfo Pro to calculate this percentage, the population for the cities must be in the STATES table.

The following example uses a region table USA.tab and a point table USCTY153.TAB that are included in the MapInfo Pro introductory data set. Run the installer from the MapInfo Pro DVD to install it.

To create a temporary column using Update Column:

1. Open the base table (USA.TAB) and the city table (USCTY153.TAB).
2. On the MAP tab, choose Add Theme.

   The Create Thematic Map - Step 1 of 3 wizard panel opens.

   
   

   

   
   
3. Click Ranges and select a template name from the list.

   This is the style of the thematic map you are creating.

4. Click Next.

   The Create Thematic Map - Step 2 of 3 wizard panel opens.

5. Click USA, this is the table you want to shade.
6. In the Field drop-down list, select Join.

   The Update Column for Thematic dialog box opens.

   
   

   

   
   

   Table to Update is already set to USA and Column to Update is automatically set to Add new temporary column.

7. In the Get Value From Table box, select USCTY153.

   If that is the only other table open, MapInfo Pro automatically displays its title in the list box.

   Note: When you create a temporary column for a thematic map, the field must be a numeric field. This is true for all thematic maps except individual values.

   Since in our example, we are looking for the percentage of the population living in urban areas in the United States, we need to calculate the total of the USCTY153 population; that is, we must calculate the total of the population of each city in a each state. We need to put that sum into the temporary column.

8. In the Calculate box, choose Sum.
9. In the of box, choose Tot_pop.

   To put the data from the USCTY153 table into the temporary column of the USA table, there must be a link between the two tables that MapInfo Pro can use to access the data. MapInfo Pro can often make this link automatically. In this example, both our tables have a State field.

10. Click Join.

    The Specify Join dialog box opens.

    
    

    

    
    

    When you choose Join in the Update Column for Thematic dialog box, you can see that MapInfo Pro has already set up the Specify Join dialog box with the STATE fields from both tables. If the join were not calculated automatically it would be necessary to specify the matching fields or geographic join.

11. Choose OK.

    MapInfo Pro calculates the sum and returns you to the Thematic - Step 2 of 3 dialog box. The Field list box displays the temporary column you created: SumOfTot_pop.

    However, before we create the map, we still need to calculate the percentage of the total population of each state that is urban. That information does not exist as a field in the table, so you must build an expression to generate it.

12. In the Field drop-down list, select Expression.

    The Expression dialog box displays.

    
    

    

    
    

    The expression SumOfTot_pop/Pop_1990 * 100 will give you the answer as a percent.

13. In the expression box, type:

    SumOfTot_pop/Pop_1990*100

14. Click Verify to ensure that your syntax is correct, and then choose OK.

    The Create Thematic - Step 2 of 3 dialog box shows the expression you created.

15. Click Next.

    The Create Thematic Map - Step 3 of 3 wizard panel opens.

    
    

    

    
    
16. Click Ranges and choose either Equal Count or Equal Ranges to customize the ranges, whichever gives you the best representation of your data.

    Use Round By to round to a decimal place or whole number. Customize the styles to best illustrate your analysis by clicking the Styles button. Customize your map legend by clicking the Legend button.

17. Click OK

The Map window redraws with your thematic.

For details about using point or line objects to represent thematic variables, see About Bivariate Thematic Mapping.