Friday, November 6, 2009

Finding out the digitized direction with a line style

In some GIS applications, it is necessary for the lines to be digitized in a certain direction. For example, in terrain modelling, lines representing drainage lines should be digitized from up to downstream. A simple trick to find out the direction of the digitized lines is to display an arrow head. I found Global Mapper to be very easy to assign a directional arrow line style to line features. All you have to do is define a new line type with the directional arrow style, then assign the line type to your line features.

  1. In Global Mapper, select Tools > Configure.

    The Configuration dialog box appears.


  2. Click the Line Styles tab if it is not active. Click New Type.

    The Setup Line Type Information dialog box appears.

  3. In the Type Name field, type in a name e.g. DigitizeDirection.

  4. In the Style drop down list, scroll down with the arrow down key and observe the sample display. Choose the style that has the arrow pointing to the right, e.g. Solid with Arrow P... (Sorry the name is too long to read from the dialog box).



  5. Click OK.

    The new line type is added.


  6. Click OK.

Now you can assign this line type to new or existing line features. If you digitize a new line feature, the following dialog box will pop up at the end of the digitizing.

In the Feature Type drop down list, choose the new line type created earlier e.g. DigitizeDirection. Click OK. As shown in the figure below, the line feature is stylized with an arrow head pointing in the digitized direction.


If the direction is incorrect, then you need to reverse the order of the line feature's vertices.

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