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Map Room Home page | |
written by Nigel
James
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MAPINFO How to... | |
No. 3: Mapping Thematic data by postcode areas, districts etc | |
(References to tables, folders etc., are not applicable outside the Map Room, so if you are located elsewhere, you should substitute your own) | |
This guide explains how to use MapInfo to map thematic data by postcodes. MapInfo How to No.1 should be used for step-by-step instructions on creating maps and layouts. If you are mapping locations by postcode (point data), see MapInfo How to no. 19 |
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1. Open a postcode boundaries table. This should be the polygons version to map thematic data. Click the Open Table button (or File/Open table), change to drive D: then open the Postcodes folder. Open the High folder (high resolution) then open the Polygons folder. 2. Open the Area folder, then open the file hap_r26.tab. 3. Click the right mouse button when the pointer is on the map window, then click View Entire Layer on the popup menu. 4. Zoom into the Oxford area, then open the Layer control. Select the hap_r26 table and click the Autolabel checkbox (4th box). Click OK to display the area codes on the map. 5. Zoom in again so that OX fills the window. 6. Click the Open table button (or File/Open table) and go back to the Polygons folder. Open the Districts folder and open the table hdp_r26.tab to add districts to the map. 7. Autolabel the districts layer (as in step 4). 8. Zoom in on the districts OX 1, OX 2, OX 3 and OX 4. 9. Now you can create a simple data table. Click File, then New Table. Select Open New Browser only. Uncheck Open New Table (we are just creating a data table, not another map layer) and click Create. 10. You will now see the New Table Structure dialog. In this example two fields are required: postcode and data value. 11. Enter the first field details by entering the name as Postcode and the type as character. Leave size at 10. 12. Click Add Field and enter the second field as name: Value and type: float. 13. Uncheck the Table is mappable box - we are creating a data table only and it will not be mappable on its own. 14. Click Create. Save the table in your folder as Postcodes.tab (see MapInfo How To No.1 if you do not know how to create your own folder. 15. The map window will hide and the new table appears at the top left of the screen. 16. There will be four records to enter, so four rows will be needed. Click on the table with the right mouse button and click New row on the popup menu. Repeat three more times (rows can also be added one at a time if preferred). 17. Click in the Postcode field of row 1. Enter OX 1 (note the space between OX and 1, if it does not match the map label exactly the data will not display). To see the map and the table side-by-side, open the Window menu and click Tile windows. 18. Click in the Value field and enter 100. 19. Repeat steps 17 and 18 with the following data: OX 2 and 75; OX 3 and 50; OX 4 and 25. 20. Click the Browser window tile bar if it is not already the active window (blue bar) and save the table. Do not close the browser window. 21. Click the map window title bar if needed, to make it the active window. Maximise the window, then click Map on the menu bar and then click Create Thematic map (if Map does not appear on the menu bar then the window is not active). 22. Creating a thematic map takes three steps. In step 1, select Ranges and then Solid Green Dark-Light. Click Next. 23. Now you can link the data to the map. Select the district table (hdp_r26) in the Table box, then click the arrow next to the Field box and click Join… in the dropdown list. 24. In Update Column for Thematic (MapInfo is creating a hidden, temporary column in the map table to hold the data) select your table (Postcodes) in the Get Value for Table list. In the Calculate value of box select Value from the dropdown list. Click OK. 25. Step 3 confirms your selections. Click Next. 26. The legend is now displayed. Click OK and the data will be mapped. Note all other postcodes show the lowest value. 27. Now you can put the area boundaries on top of the district boundaries. Click the map title bar if it is not active, then open the Layer Control. Move hap_r26 above hdp_r26 and its thematic layer, either by dragging it or by selecting it and using the Up reorder button. Don't click OK yet. 28. With the hap_r26 layer still selected, click the Display button, the click the Style override checkbox. Click the big button. Set Fill Pattern to none and the line colour to red. Click OK in each dialog to redisplay the map. You may need to zoom the map out to see the area boundaries. 29. Change the labels to show the data values instead of postcodes by opening the Layer Control, selecting layer hdp_r26 and clicking the Label button. In the Label with box choose Value from the list. Click OK in each dialog to redisplay the map. 30. You can also display the postcode and the value. To do this, repeat step 29 but select expression in the Label with list. 31. In the Expression dialog, click the Columns button, then click GEO_DIST (which contains the postcodes). After GEO_DIST type + then " (" [note the space after the first "]. Click the Columns button again and click Value. Type + ")" to finish the expression. 32. The expression should now read: GEO_DIST+" ("+value+")" 33. Click OK in all dialogs to display the postcodes with the values in brackets. 34. To show just the four postcode districts with values and the rest blank, Click the OX 1 polygon on the map to select it, then hold down the shift key and click the other three districts. If you cannot select them (because the area table is on top), open the Layer Control and make the layer hap_r26 unselectable by unchecking the Selectable checkbox (the 3rd one along). Leave the four districts selected for now. 35. With the four districts selected, go back to step 21 and repeat the process to create a thematic map, but this time instead of selecting the entire table (hdp_r26) in step 23, choose selection from hdp_r26. Make sure you still select Value for the value box. Choose a different colour range this time and create the thematic layer. 36. The new layer will be attached to the hdp_r26 layer, but above the previous thematic layer. You can then choose the layer to be visible by making the upper layer visible or not in the Layer Control (1st checkbox). |
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This is a brief and specific guide to this topic, for more general information, see: MapInfo - an easy guide for new users | |
Nigel
James
Bodleian Library 2001 |