Managing polygon within polygon

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There are situations where it is necessary to draw one or more polygons within another bigger polygon. Typical examples are islands and park lakes. http://www.malsingmaps.com/tutorials/MapRef/IslandOverSea.gif http://www.malsingmaps.com/tutorials/MapRef/LakeOverPark.gif

If you merely draw one polygon on top of the other, the effect of the map is uncertain. It is possible that the bigger polygon (sea or park) may overlap the polygon within (island or lake). The smaller polygon will not be displayed.

GPSMapedit has a function for you to create a 'hole' within the bigger polygon so that there is no overlapping of polygons.

http://www.malsingmaps.com/tutorials/MapRef/MinusPolygon.gif

  1. Draw the sea polygon
  2. Draw the island polygon
  3. Select both by clicking the Select Objects button and dragging the rectangle across both polygons
  4. Right-click on the polygons. Select Subtract Polygons


There is another method to manage polygons, by controlling the polygon draw priority using type customisation.