Hawth's Analysis Tools for ArcGIS

SpatialEcology.Com

 You are here: Home > Hawths Tools > Tools Descriptions & Help

 Summary

DISTANCE BETWEEN POINTS TOOL (BETWEEN LAYERS)
Input: two point layers
Output:various tables representing distances or summary statistics of distances between points
Features:

  • a tool with several options to tailor the output
  • the output can take four forms: a complete distance matrix (a table of the distance between each source and taget point) in either linear or tabular formats, a summary statistics table of the distances (designed for large sample sizes), and a table listing the closest point (their ID's and the distance from the point in question)
  • provides an option to process only the selected features in each point layer
  • requires a unqiue ID field to be specified, and although it is best for this field to be a long integer type, the program will also process text (string) ID's

Limitations:

  • the output is a comma delimited textfile (.csv), no other formats are supported
  • when creating the full distance matrix table, if you have more than 255 columns you may not be able to open the table in certain other software
  • does not work with data in a Geographic Coordinate system (distances calculated using spherical coordinate systems are not valid because the x and y axes are not proportional across space)
  • does not perform on-the-fly projection changes, so the source files MUST be in a projected coordinate system (users cannot just change the projection of the map window)


[Click for larger view]

 Example

Figures A-D. The linear format of the point-distance matrix is shown in Figure A, and the tabular (NxN) format of the same table is shown in Figure B. (The red arrows are intended to represent that only a small portion of the full output table is shown in the picture). The ouput can also take the form of a statistical summary of the distance matrix (C). Finally, the user can elect to list the N nearest neighbours in the target layer to each point in the source layer (D). Using this option the unique ID and distance of each of the N closest points is listed in the output table.

 Help

Getting started. Two point layers must be loaded into ArcMap in order to use this tool. The point layers MUST be in projected coordinate system like UTM or SPC, not a Geographic (Lat/Lon) coordinate system. If either of your point layers is an event theme and you are experiencing problems, try making it a shapefile and trying again (right click on the event theme in the Table of Contents, select Data, then Export Data).

Selected a unique ID field When you select a point layer from the drop-down box, all possible unique ID (UID) fields are listed in the next drop-down box. A UID field will ideally be an integer field, although the tool can accomodate text (string) fields. Given the choice, select an integer field.

Using only selected features. When you select a point layer from the drop down list the program checks to see if there are selected features in that layer, and enables the "Use selected features only" option. If you select this option then only the selected features will be processed.

Listing nearest neighbours. Use the "Find the top N closest points" number box to define how many points will be listed. If you select just 1 point, then all that will be listed is the single closest point. If you select 5, then the top 5 closest points are listed in order of their proximity, with the closest points always occuring first in the list (as you will be able to see from the distances that are also output to that table). Note that in the case of points that are equidistant, one of those points is selected arbitrarily as the closest.

Processing time. If you have a large number of points (>100,000), this program may take a considerable amount of time to run. It is recommended that you try running a test on a smaller sample before embarking on more ambitious analyses.

Home | Articles | Services || Hawth's Tools:  Overview | Description | Download | FAQ