Polygonise Contour Line

Owned by Wojciech Mozolewski
14 Dec 2020
3 min read

This tool is used to create a polygon showing part of the map below or equal to a set height in a given area. It is especially useful when trying to identify areas which may “pool” with excess water. To explain how to use this tool we will use the Landform PANORAMA layer, which is part of the Ordnance Survey Open Data.

Please select the Polygonize Contour Line tool. The whole operation takes 3 steps:

 

 

Step 1 of 3: Select a height reference point.

This is the first step. It allows you to set a height reference point. The height of this point will be used in the final calculations. Please use the mouse cursor to select the location and confirm it by clicking the left mouse button. You can also use the context menu to enter the exact X and Y coordinates.

 

 

Step 2 of 3: Select a centre of contour polygonization area.

In this step, you have to set a centre of contour polygonization area. Please use the mouse cursor to select the location and confirm it by clicking the left mouse button. You can also use the context menu to enter the exact X and Y coordinates.

Step 3 of 3: Select a radius of contour polygonization area.

This is a final step. Please move the mouse cursor to set a radius for the Polygonize Contour Line operation or set the radius using the context menu.

 

 

Use the left mouse button to accept the radius. A Polygonize Contour Line window will appear.

 

 

  1. In the Polygonize Contour Line window, you can see and change all settings Polygonize Contour Line operation. It contains 4 fields:

  2. Height (in metres):
    This field displays the height of the reference point (selected in step 1 of 3). You can enter a new value by clicking the field or using small arrows next to the value.

  3. Centre X:
    Here you can see the X coordinate of the centre of contour polygonization area (selected in step 2 of 3). You can enter a new value by clicking the field or using small arrows next to the value.

  4. Centre Y:
    Here you can see the Y coordinate of the centre of contour polygonization area (selected in step 2 of 3). You can enter a new value by clicking the field or using small arrows next to the value.

  5. Radius (in metres)
    This field displays the radius of contour polygonization area. You can enter a new value by clicking the field or using small arrows next to the value.

If you accept all settings please click the OK button to start the Polygonize Contour Line operation. After a few seconds, you will see the result.

 

 

The grey area presented on the screen above shows part of the map below or equal to a Height value set in Polygonize Contour Line window.

The area created by the Polygonize Contour Line tool is, in essence, a map annotation and can be edited by tools from the Annotations tab.

You can change the style of the annotations by using the Gallery / Change Style tools or by setting a default style in Global/Inheritable User Setting.