How do you make a velocity map in ArcGIS?
March 17 2009 |
Hello, my question is how do you make a velocity map in ArcGIS?
Mapping Center Answer:
Assuming that you have point data that has a field for direction or bearing and another for magnitude or speed, you can create a velocity map as a point feature map (as in the map at the left in your attachment) or an isoline map (as in the map at the right in your attachment.) To create the velocity map as a point feature map:
- In the Layer Properties for the points layer, on the Symbology tab, show Quantities -> Graduated Symbols.
- Set the Value field to the speed or magnitude field in your points layer.
- Set the symbols to whatever size works for your map. For the map below, I used symbol sizes from 4 to 18.
- Click the Template button, then click Properties.
- Change the Type to Character Marker Symbol. Change the Font to ESRI Arrowhead. Select an arrow that will look good on your map and change any properties you want for it.
- Click OK to get back to the Symbology tab.
- Click the Advanced button at the bottom right. Click Rotation. Set the field to be the direction or bearing field. Be sure to use the Rotation Style appropriate for your type of data.
- Click OK to exit all dialog boxes.
To create a velocity map as an isoline map, you will need to have the Spatial Analyst extension:
- In ArcToolbox, open the Spatial Analyst tools and select an interpolation tool from the Interpolation toolset. I used IDW to create the raster below.
- In ArcToolbox, open the Spatial Analyst tools and select the Contour tool from the Surface toolset. Use the interpolated raster as the input. Set the contour interval to whatever makes sense for your map. Here is the result, showing 1) the contours, 2) the points, and 3) the interpolated surface.
At this point, you could also create a hillshade for the interpolated surface. You will again need to have the Spatial Analyst extension:
- In ArcToolbox, open the Spatial Analyst tools and select the Hillshade tool from the Surface toolset. Use the interpolated raster as the input.
- Set the transparency of the interpolated raster (and the contours, if you want) to about 50%. Here is what the result looks like with the hillshade added.
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