Point distance output in wrong units

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06-15-2010 04:57 AM
SarahBowden
New Contributor
I'm using the Point Distance tool to calculate the distance between points in 2 datasets within 1 km of each other. However, my output is in (I'm assuming) decimal degrees even though I specify km or m. I have tried projecting in several different coordinate systems (State Plane, Behrmann, NAD83, etc.) with no change. I read a previous post on the same topic and the suggestion was to change the projection, so does anyone have another suggestion?

Thanks,

Sarah Bowden
1 Solution

Accepted Solutions
DanLee
by Esri Regular Contributor
Esri Regular Contributor
The values in the outut field, DISTANCE, of Point Distance tool are ALWAYS in the same units as the input features. To find out what your input feature units are, you can right-click the input feature class, choose "Properties...". Under the "XY Coordinate System" tab, you should see the Name of the coordinate system; in the Details section, you should see "Linear Unit: ..." - e.g. Meter or Feet. That is your feature unit. If your data is not projected, you should see the name like GCS_xxx and your data is in decimal degrees. When your data is in a GCS, you can tell by the DISTANCE values, such as 0.439578439. So, can you check for your input data - what is shown under the "XY Coordinate System" tab?

If your data is in GCS, the right thing to do is to project it to a local coordinate system (as you tried) before using the Point Distance tool or any spatial analysis tool.

The units you specify for the Search Radius is only for your convenience of thinking about the search distance; it does not affect the units for the values in the output field DISTANCE.

If you need the DISTANCE values in different units, you can do the following:
1. Use the Add Field tool to add a double type field, e.g. DIST_KM.
2. Use the Calculate Field tool with the appropriate expression to convert the values in DISTANCE to new values in the desired units. Take a look of the examples in the following help topics about how to specify the expressions.
http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/Calculate_Field/00170000004m000000/
http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/Calculate_Field_examples/00170000004s0...

Hope that helps.


Edits: I have requested the clarifications on units to be added to the tool references.

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3 Replies
curtvprice
MVP Esteemed Contributor
I'm using the Point Distance tool to calculate the distance between points in 2 datasets within 1 km of each other. However, my output is in (I'm assuming) decimal degrees even though I specify km or m. I have tried projecting in several different coordinate systems (State Plane, Behrmann, NAD83, etc.) with no change. I read a previous post on the same topic and the suggestion was to change the projection, so does anyone have another suggestion?


Sarah - make sure your projection is "taking". I think the best processing flow for doing this interactively is

1- set the data frame in arcmap to a coordinate system that is appropriate for distance (say, UTM, state plane)
2- right click the layer for each data set in tern and export to a temporary feature class or shapefile, be sure and choose to export in the data frame coordinate system
3- open the point distance tool and open "Environments" to make sure the coordinate system output is default
4- go ahead and run the tool.
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DmontierAragão
New Contributor
Hi all,
i made an analysis using point distance, but i have a doubt with the output of the point distance.
I don't know the units of the output, i need the values in kilometers, but how do it?

Thanks in advance...
0 Kudos
DanLee
by Esri Regular Contributor
Esri Regular Contributor
The values in the outut field, DISTANCE, of Point Distance tool are ALWAYS in the same units as the input features. To find out what your input feature units are, you can right-click the input feature class, choose "Properties...". Under the "XY Coordinate System" tab, you should see the Name of the coordinate system; in the Details section, you should see "Linear Unit: ..." - e.g. Meter or Feet. That is your feature unit. If your data is not projected, you should see the name like GCS_xxx and your data is in decimal degrees. When your data is in a GCS, you can tell by the DISTANCE values, such as 0.439578439. So, can you check for your input data - what is shown under the "XY Coordinate System" tab?

If your data is in GCS, the right thing to do is to project it to a local coordinate system (as you tried) before using the Point Distance tool or any spatial analysis tool.

The units you specify for the Search Radius is only for your convenience of thinking about the search distance; it does not affect the units for the values in the output field DISTANCE.

If you need the DISTANCE values in different units, you can do the following:
1. Use the Add Field tool to add a double type field, e.g. DIST_KM.
2. Use the Calculate Field tool with the appropriate expression to convert the values in DISTANCE to new values in the desired units. Take a look of the examples in the following help topics about how to specify the expressions.
http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/Calculate_Field/00170000004m000000/
http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/Calculate_Field_examples/00170000004s0...

Hope that helps.


Edits: I have requested the clarifications on units to be added to the tool references.