Pima County Geographic Information Systems

MapGuide Tutorial: Creating and Using Buffers

Autodesk MapGuide's buffer feature lets you identify map features within a certain distance of one or more other map features. A common use is to find all parcels within a certain distance to create owner notification lists. We'll use parcels in this tutorial, although buffering can be used with other map features, like streets, as well.

While this tutorial may look long and difficult, once you go through it a couple of times you'll be able to create a buffer and mailing list in minutes.

The process follows these major steps:

• Choose the "Selection Mode".
• Select one or more features (usually parcels or streets) to be buffered.
• Create the buffer zone by specifying the desired distance.
• Select parcels within the buffer zone.
• Create a report of mailing addresses for those selected parcels.

Choose the Selection Mode

Choosing the Selection Mode is a technical, but necessary choice to get the parcels you want within or partially covered by your buffer. The choices are Centroid or Intersection.

Choosing Centroid selects parcels whose "middle" points fall within the buffer. If most of a parcel falls outside the buffer area, but some of the parcel falls within, then this parcel will not be selected with Centroid mode because the Centroid or "middle" point of the parcel lies outside the buffer area.

Choosing Intersection selects parcels that are entirely within the buffer or parcels crossed at any point by the buffer boundary. Intersection mode selects more parcels at the perimeter of the buffer than Centroid mode. If even the smallest area of the parcel is within the buffer, then the entire parcel is selected. If parcels are large, this can greatly expand the area of the selected parcels. However, if you wanted to notify owners of parcels within 300 feet, then it makes sense to notify those whose parcels are partially within the 300 foot limit because part of their parcel is affected. Intersection is probably the best choice for making notification lists.

• Use right-click, Help, Preference... to bring up the Preferences dialog box.
• Select the desired Selection Mode, either Centroid or Intersection.
• Click "OK" to close the Preferences dialog box.

Selecting the Features to be Buffered

• Zoom to the area of interest. (Zoom in close enough so that the parcel layer is visible.)
• Select a parcel to be in the center of the buffer by clicking on it. The parcel turns color indicating that it is selected.
  • To select additional parcels to be in the center of the buffer, hold the SHIFT key and click on the parcel(s) to be added. Selected parcels may be adjoining or separated. If selected parcels are separate, then the finished buffer is created for each separate group of one or more parcels.
  • To "deselect" a selected parcel, hold the SHIFT key and click on the parcel to be deselected.
  • To clear all selections and start over: right-click, Select, Select Clear

Creating the Buffer Zone

• Right-click, Buffers, Create Buffer... to bring up the View Buffer dialog box.
• Select the units for the Buffer Offset Distance: mi, Km, ft, or m (miles, kilometers, feet or meters).
• Enter the desired buffer offset distance. I.E. How far to buffer.
• Leave the box checked for "Construct one buffer for all selected map objects." Any buffer areas that run into each other will be merged. This is normally what you want.
• Type over "Buffer layer" in the "Create buffer on" box to name your buffer area. This name shows up in the map legend. You might name it "Impact area" or simply "Quarter mile buffer".
• When you are done, the buffer area is displayed on the map. The rest of the dialog box lets you select the colors and the style of the buffer's appearance. As you change the appearance settings, an example is shown in the lower right of the dialog box.
  • Under "Fill" select None, Solid or Hatch for the interior of the displayed buffer. If you select "None", your buffer area will be shown by a line at the edge. If you select "Hatch", your buffer will have hatch lines over it's entire area. Selecting "Solid" isn't usually useful as the buffer area obscures underlying parcels.
  • Select the Color and Pattern for your fill. (Fill style "None" won't let you select Color or Pattern. File style "Solid" won't let you select a pattern.)
  • If Hatch style was selected then select the Background Mode, either Transparent or Solid. Transparent lets you "see through" the hatch and is usually the best choice. Choosing Solid also lets you select the color behind the hatch lines.
  • Lastly, see that "Edge" is checked which puts a line around the edge of the buffer area. Select the style (line, dashed line, etc.), color, and thickness of the line using the displayed sample as a guide. A solid edge line with thickness 2 or 3 usually works best.
• You're done with this dialog box, so press "OK" and see your new buffer displayed! Pan or zoom as needed to position the buffer in the map frame. If you just wanted to see the buffer zone, then stop here. You're done!

Selecting Parcels Within the Buffer Zone

• Click on the buffer itself to select it. It changes color.
• Right-click, Buffers, Select Layer Within Buffer... and a list of one or more layers is shown.
• Click on "Parcels - Pima" and click "OK" to see the parcels in the buffer area. The number of parcels selected varies depending on whether the Selection Mode was set to Intersection or Centroid earlier.
• You may find extraneous areas selected, such as street right-of-way. These may be long since one street can flow into many others. Use SHIFT-click to "tune up" your selected areas. To remove street righ-of-way or other undesired areas, press SHIFT and click on them. To add a parcel that was excluded but you really want, press SHIFT and click on it.

Creating a Report of Mailing Addresses

Now that you have all the desired parcels selected, see MapGuide Tutorial: Creating Reports and MapGuide Tutorial: Mailing Labels to create a list of mailing addresses.