# Measuring distance between points in ArcMap - what coordinate system to use?

This is a basic -newbie - question. I have some handwritten data points taken off a GPS - so I am assuming they are in WGS 84, and I want to load them in ArcMap 9.3, via excel, and measure the distance between them (they are transects). I would like to know how best to maintain accuracy, and what format the data the coordinates should be when I load them into ArcMap.

The coordinates look like: 39. 51 550, 148.16 841 but the way they have been written they could be 39. 51 .50, 148.16.841 or 39 51.550, 148 16.841. Do these look like WGS 84 coordinates and what is the best way to input them into excel? Do I have to set or reset the projection in ArcMap before I take the measurements?

As you can see I am not confident with the basics of the coordinate system and projection system so any help and tips would be appreciated.

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The coordinates look like degrees decimal-minutes. You'll need to convert them to decimal degrees to import them as WGS84. Do this in excel and then add the table to ArcGIS as an Excel table. Then create an XY Event layer from the coordinates. Finally, convert this to a geodatabase feature class of shapefile.

If you want to measure the distances between points on a one by one basis, your best bet is to use the measure tool's geodesic option. See this topic for more detail: http://webhelp.esri.com/arcgiSDEsktop/9.3/index.cfm?TopicName=Measuring_distances_and_areas

Craig

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In addition to what @Craig Williams has suggested after you have your layer defined in the WGS84 coordinate system you should then re-project your layer to a Projected Coordinate System which is better for measuring purposes.

http://blogs.esri.com/Dev/blogs/arcgisserver/archive/2010/03/05/Measuring-distances-and-areas-when-your-map-uses-the-Mercator-projection.aspx

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That article is correct in pointing out you can use a different projection for measurements, depending on the purpose, but its specific examples are misleading and poor. In particular, the "geodesic option" will, for general purposes, be consistently more accurate for large distances than any projected coordinate system. – whuber Aug 1 '11 at 13:32