Determining the Spatial Accuracy of Polygons Using Buffer Overlay


This is the 7th post on on my paper “A Method for Determining and Improving the Horizontal Accuracy of Geospatial Features” Other posts on this topic:

6. Five Methods for Determining the Spatial Accuracy of Lines
8. The Final Solution

Buffer Overlay is a geospatial analysis technique that creates a buffer around a control line, the buffer is then used to clip a test line, the lengths of both lines are compared and if the test line is significantly shorter than the control a larger buffer is used. When test and control lengths are equal the test line can be said to be the size of the last buffer applied.

In our case the control is parcel line work and the test are permits. However, it is not practical to buffer the line work of an individual parcel and then clip the permits because not all parcels have permits. So we will have to reverse the procedure and buffer the test line and find the length of control within the buffer. A more complete description of the procedure is as follows:

  • Convert parcel polygons to parcel lines
  • For each permit
    • Buffer from .5 ft to 60 ft @ .5 ft intervals
      • Clip the parcel lines (control) using buffer
      • Drop dangling nodes (where length = buffer)
      • Calculate the Cumulative Probability (CP)
      • CP = (Length of Clipped Parcel Line/Perimeter of Permit)
      • If CP >= 1
        • Horizontal accuracy is +/- buffer distance
      • Else If CP <= 0.999 and buffer < 60
        • Next buffer

The results of this procedure is the creation of individual probability curves for each permit as shown in the image and video below.

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