How to create polygon maps

In the text below, the word 'code' will be used for the class names, IDs, or values of segments.

According to the ILWIS concept, segments with different class names, IDs or values can be stored in a segment map.

From each segment code or set of codes, different polygon maps can be created by using a mask. It is advised that you have a separate label point map for each set of segment codes from which you want to create a polygon map.

For a general introduction on creating maps, refer to How to create maps.

For more information on using a digitizer, refer to How to set up a digitizer and start digitizing and Segment editor : functionality.

Steps to obtain a polygon map:

Start the segment editor: when you create a new segment map, the segment editor is automatically started. To edit an existing segment map in a map window, open the Edit menu, choose Edit Layer and select the segment layer from the cascading menu.

Start the point editor: when you create a new point map, the point editor is automatically started. To edit an existing map, display the point map in a map window, open the Edit menu, choose Edit Layer and select the point layer from the cascading menu.

In the segment editor: digitize the segments. When you want to create multiple polygon maps from one segment map, you have to code your segments in such a way that you can select sets of codes by using a mask later on.

In the point editor: digitize a label point within each polygon boundary. The label is the class name, ID or value of each future polygon.

Tip:

It is recommended to add your segment map as a data layer to the point editor, and regularly redraw the point map . Changes in the segment map will then be reflected in the point editor. In this way, you can easily verify whether each future polygon has a label point.

In the segment editor, from the File menu, select Check Segments, Self Overlap, and subsequently Check Segments, Dead Ends, and Check Segments, Intersections.

Correct possible errors.
In the segment editor, from the File menu, select Polygonize.

The Polygonize Segment Map dialog box appears.

select the mask for the segments which should be used for polygonization;
select the label point map;
select a name for the output polygon map.

Segments will be checked and if no errors occur in your segment map, the topology will be build and polygons are named according to the label point map.

Note:

If you digitize different segment codes in one digitizing session (for example: soil units, districts, roads etc.) make sure you select the right mask for polygonization. You can repeat the procedure of creating polygons; each time specify another mask, another label point map and a different output polygon map name.

Tip:

To check after polygonization whether all polygons have a class name, ID or value, you can use the Find Undefineds option from the Edit menu of the polygon editor.

You may also use the Polygons to Points operation, see Polygons to Points : functionality.