Simplifying Shapes

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MPSuperShape can simplify the selected shapes. The simplification process removes vertices (points) from the shape outline whilst trying to preserve as much of the shape's general outline as possible. This is useful if your map has a number of shapes with large numbers of vertices that are slowing MapPoint's performance. Use the simplify operation on shapes which are more detailed than necessary. By simplifying these shapes, the size of the map (ptm) file is reduced and MapPoint will run quicker and more smoothly.

 

Removing vertices from a shape will almost always result in changes to the shape's outline. Usually small changes are acceptable, but large changes are not. MPSuperShape allows you to specify the maximum acceptable change, as a linear distance. This is called the tolerance. A vertex will only be removed if the resulting lateral change in the shape's boundary is less than this tolerance distance.

 

To simplify the selected shapes, select Simplify from the popup menu, to display the Simplify Shapes dialog box:

 

simplify_start

 

When the Simplify Shapes dialog box is displayed, it scans the selected shapes, counting the number of vertices. The number of shapes and the total number of vertices are displayed in the box in the lower half of the dialog box.

 

Enter the tolerance. This is maximum allowable change in the shape, measured as a linear distance. The tolerance is specified using MapPoint's current distance units (miles or kilometers). A tolerance of 1 mile has been specified in this example, so a vertex will only be removed if it the shape's outline is displaced by less than 1 mile.

 

It is difficult to gauge the effects of a specific tolerance, so an Estimate button has been supplied. Select this to estimate the resulting number of shapes and vertices for a specific tolerance. Note that some shapes might disappear completely if the tolerance results in a shape with less than 3 vertices. Here is the Simplify Shapes dialog box, after the Estimate button has been pressed:

 

simplify_estimate

 

For this example, a tolerance of 1 mile reduces the number of vertices from 169 to 62, but retains both shapes.

 

When you have chosen a suitable tolerance, press OK to apply the simplification process to the selected shapes. Note that the OK button is only enabled after the Estimate button has been pressed.  Large numbers of shapes may take a few seconds to simplify, so progress is displayed in the box in the lower half of the Simplify Shapes dialog box.

 

Note: In common with other MPSuperShape operations, ellipses and rectangles will be converted into freeform shapes before the simplification process is applied. This can result in shapes that are more complex and use more memory. Therefore it is generally not recommended that the simplification operation is used on ellipses and rectangles for most applications.