The Buffer Wizard in ArcMap

By Margaret Maher, Esri Support Services Specialist

Buffer thumbnail

There are two tools you can use to create buffers in ArcGIS—the Buffer tool in ArcToolbox and the Buffer Wizard. Buffers are used not only in analysis of distances and areas around point, line and area features, they are also used in mapping to achieve a number of cartographic effects, such as coastal vignettes. Since there are two tools and multiple methods you can use to create buffers, and each have their particular strengths and weaknesses, we thought it would be good to review these for you. In a related blog post, we’ll describe the tools and methods, how they differ and what you need to consider when using them.As an introduction, this tool review is an extension of the work that our colleague, Tom Bole of the ArcMap Team, did a few years ago in response to the map that appeared in The Economist on May 3, 2003. This map showed the countries that can be reached by North Korean missiles with different ranges.

Economist 05-03-2003

The map was corrected in the May 17 issue of The Economist.

Economist 05-17-2003

The buffers in these articles are clearly for analysis purposes, so knowing how they are generated and how accurate the results are is imperative. Although there is a little more leeway with buffers for cartographic effects, it still behooves the good map maker to know how ArcGIS create buffers. So this first blog post focuses on the Buffer Wizard. In the next one, we’ll discuss the Buffer Tool in ArcToolbox, as well as the variations between the two tools. (Thanks to Tom for the map graphics in this blog!)

The ArcMap Buffer Wizard functions evolved from tools developed for the ArcView GIS 3.x environment. By default, The Buffer Wizard uses a temporary on-the-fly projection to minimize distortion in the output buffers. Many users migrating from ArcView GIS 3.x to ArcGIS Desktop are not aware of the effects of spatial reference on buffer results, and might not adjust the spatial reference of the ArcMap Data Frame to an appropriate coordinate system. The default setting of the Buffer Wizard adjusts for this by using a temporary coordinate system to construct geometrically correct buffers.

To add the Buffer Wizard to ArcMap, go to Tools > Customize > Commands tab. In the Categories window on the left, scroll down and select Tools. From the Commands window on the right, select the Buffer Wizard tool, then drag and drop the tool onto any toolbar displayed in the ArcMap window (figure 1).

Figure 1 - Buffer Wizard

Figure 1. Location of the Buffer Wizard tool in ArcMap.

In ArcGIS Desktop versions 8.3 and earlier, the Buffer Wizard was included in the Tools dropdown menu, but was moved to the Customize dialog at 9.0.

How the Buffer Wizard works with coordinate systems

The ArcMap 8x Buffer Wizard uses a temporary spatial reference system called the Buffer Processing Coordinate System, or BPCS, when creating buffers. There are four options available for the BPCS, and you can change the setting in ArcMap Advanced Settings Utility > Miscellaneous tab. Figure 2 illustrates one page of this dialog.

The utility is located in the ArcGIS install folder at UtilitiesAdvancedArcMapSettings.exe. ArcMap must be closed in order to open the dialog. Administrative permissions are required to change settings, because entries change Registry settings on the computer. Any changes should be made with caution.

Figure 2 - ArcMap Advanced Settings

Figure 2. The ArcMap Advanced Settings Utility dialog Miscellaneous tab, with the Buffer processing coordinate system options displayed in the dropdown. “Feature set optimized coordinate system” is the default setting for the Buffer Wizard when ArcMap is installed.

Here is a detailed description of each option for the Buffer Processing Coordinate System:

  • Feature set optimized coordinate system – This is the default setting. The BPCS is based on the spatial distribution of the buffered features. A temporary Hotine Oblique Cylindrical projection is calculated based on the position of the features being buffered. Once the buffer is created, the buffers are reprojected and saved in the coordinate system of the ArcMap Data Frame. This setting helps minimize distortion regardless of the spatial reference of the Data Frame. If you are buffering from a selected subset of features, the centerline of the temporary projection is calculated using the subset of features.
  • Feature optimized coordinate system – A BPCS is created for each feature being buffered, and each is based on an azimuthal equidistant projection created for each separate feature. For lines and polygons, the center point of each feature is calculated. Once created, the buffers are reprojected and saved in the coordinate system of the ArcMap Data Frame. This setting also helps minimize distortion regardless of the spatial reference of the Data Frame. Though performance will be slower with this setting, it does offer the least distortion when buffering point features.
  • Coordinate system of the data frame (output) – The BPCS is based on the coordinate system of the Data Frame. Accuracy of the buffers will depend on how appropriate the coordinate system of the Data Frame is for the features being buffered. To obtain maximum accuracy for buffers using this setting, the ArcMap Data Frame needs to be set to a custom equidistant projection with parameters defined to center the coordinate system in the middle of the data. For more information on different projections and their properties, and creating custom projections in ArcMap refer to Knowledge Base articles 24646 and 30583 on the Esri Support Center (http://support.esri.com/).
  • Coordinate System of the feature class (input) – The BPCS is based on the coordinate system of the features being buffered. Once created, the buffers are reprojected and saved in the coordinate system of the Data Frame. Accuracy of the buffers will depend on how appropriate the coordinate system of the feature class is for the features being buffered, as well as the coordinate system of the ArcMap Data Frame.

Given the information above, you will need to decide how you want the Buffer Wizard to perform, and what results you need when you buffer features. Here are some issues to consider that primarily pertain to buffering points, but apply to buffering lines and polygons as well.

People instinctively expect buffers around points to be round. However, if the ArcMap Data Frame is set to a Geographic Coordinate System like GCS_North_American_1983 or GCS_WGS_1984, buffers that are geometrically correct, and measure the same distance from the center point to the buffer in any direction, will display as ovals.

Is your map being prepared for GIS professionals who will understand the buffer display, and how the buffers may be “stretched” east to west if a Geographic Coordinate System is applied to the Data Frame?

Is your map being prepared for people who are not well-versed in GIS principles, and will expect to see round buffers? If this is your situation, it would be advisable to change the projection of the ArcMap Data Frame to a projected coordinate system that used units of meters or feet. This might be UTM, State Plane or another projected coordinate system. Changing the projection of the ArcMap Data Frame will result in the geometrically correct buffers displaying as round circles, meeting expectations for people who will be viewing the map.

The examples below, created using large buffer distances, demonstrate some of the visual distortions introduced when displaying buffers in a Geographic Coordinate System, as well as the inaccuracy introduced when creating buffers when the calculation is based on a GCS.

Buffer Wizard Test using ArcMap

Three buffer rings of 5,000 km each around a point (Pyongyang) and polygon (North Korea) were created using 3 different BPCS settings and 2 different Data Frame coordinate systems.

In order to assess the accuracy of the buffer, major world cities are labeled with their great circle distance to Pyongyang (125.941074 E, 39.785978 N). The distances were taken from the following website – http://www.wcrl.ars.usda.gov/cec/java/lat-long.htm.

Distance Table

BPCS: Coordinate System of the Data Frame
Data Frame Coordinate System: GCS_WGS_1984

Figure 3 - Coordinate System of the data frame

Figure 3. These buffers are not accurate. Only Johannesburg is within the correct buffer ring (10,001-15,000). Buffering from the North Korean polygon gives similar results. Even though the buffer rings display as the expected circles, the buffer distances from Pyongyang are not correct.

Notice in this world view, displayed in a Geographic Coordinate System, that the North and South Poles, which are points, appear as long as the Equator. This “stretching” of data always occurs when data is displayed in a GCS. At the Equator, 1° east to west measures approximately 69 miles. At the North or South Pole, 1° measures 0 miles, since the Poles are points. The distortion in data display increases with distance north or south of the Equator.

BPCS: Feature optimized
Data Frame Coordinate System: GCS_WGS_1984

Figure 4 - Feature optimized

Figure 4. These buffers appear to be correct. Buffering from the North Korean polygon gives similar results. Notice, though, the difficulty that might occur when viewing the buffers as shown in this map. Even though the buffer rings are geometrically correct, the distortion in the buffer shapes introduced by displaying the buffers in a Geographic Coordinate System might defeat the purpose of the map for the intended audience. Compare with the display of these buffers shown in figure 7.

BPCS: Feature set optimized (temporary Hotine projection)
Data Frame Coordinate System: GCS_WGS_1984
Buffer from point

Figure 5 - Feature Set Optimized (pt)

Figure 5.  These buffers are not correct.  Note that in comparison with the great circle distances shown in the table, the cities do not lie within the correct buffer rings.

BPCS: Feature set optimized (temporary Hotine projection)
Data Frame Coordinate System:
GCS_WGS_1984
Buffer from polygon

Figure 6 - Feature Set Optimized (poly)

Figure 6. These buffers are inaccurate. Buffering from the North Korean polygon gives different results, also incorrect. Buffering at these distances creates problems for the temporary Hotine projection, and this is a limitation of this buffer processing method.

BPCS: Coordinate System of the data frame
Data Frame Coordinate System: Azimuthal_Equidistant

Figure 7 - Coordinate System of the data frame - AzED

Figure 7. These buffers appear to be accurate, and visually present the buffers in a way that is easier to understand and interpret than the presentation in figure 4.

BPCS: Feature optimized
Data Frame Coordinate System: Azimuthal_Equidistant

Figure 8 - Feature optimized - AzED

Figure 8. These buffers appear to be accurate.

BPCS: Feature set optimized (temporary Hotine projection)
Data Frame Coordinate System: Azimuthal_Equidistant

Figure 9 - Feature set optimized - AzED

Figure 9. These buffers are inaccurate. Buffering at these distances creates problems for the temporary Hotine projection, and this is a limitation of this buffer processing method.

Conclusions

  1. The default processing for the 8x Buffer Wizard has issues with large distances at the world scale. This is a limitation of using a temporary Hotine projection.
  2. The best result was achieved by using the Feature optimized option.BPCS: Feature optimized
    Data Frame Coordinate System: GCS_WGS_1984
     Feature set optimized - WGS84BPCS: Feature optimized
    Data Frame Coordinate System: Azimuthal_Equidistant
    Feature optimized - AzED
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6 Comments

  1. BruceLang says:

    Unable to locate the “buffer wizard” tool in ArcEditor 9.3 so a search on ESRI.com seems to indicate the “Production Line Tool Set (PLTS)” extension is required for this particular tool. :(

  2. abuckley says:

    To find the Buffer Wizard in 9.3, click Tools on the top bar menu in ArcMap, click Customize, then on the Commands tab, set the “Categories:” to Tools and you will see the Buffer Wizard on the right side of the dialog box in the “Commands:” list. Click and hold to drag the Buffer Wizard tool to any toolbar.

    Here is the URL for the online help about the Buffer Wizard: http://webhelp.esri.com/arcgisdesktop/9.1/index.cfm?id=378&pid=364&topicname=The%20Buffer%20Wizard%20versus%20ArcToolbox%20buffer%20tools.

  3. mickjamlm says:

    Excellent post! When will the followup posts be posted?

  4. me2 says:

    Is there an easy way for an ArcObjects programmer to take advantage of the Buffer Wizard’s Feature optimized coordinate system functionality (in ArcGIS 10 and beyond)?

    Thanks

  5. marg3002 says:

    I’m so sorry, but the Buffer Wizard functionality is not available through ArcObjects. The Feature optimized coordinate system uses the Hotine projection, though, so a custom Hotine projection, centered on your area of interest, could be created. Project your data to that custom coordinate system, then use that same projection to generate the buffers for your data. Keep in mind, though, that Hotine is not suitable for long buffer distances, so if the buffer distances are greater than, say 2 1/2 miles or so, you would want to use an Equidistant projection.