# Calculating distances in Geographic Coordinate System using ArcGIS for Desktop?

I work in a Geographic Coordinate System and using the "Generate Near Table" tool in ArcGIS 10.2 for Desktop.

I want to calculate the distances that each feature of the point layer has to the closest point (vertex) of the coastline (the coastline is a line shapefile).

The distance method I use in GEODESIC, but I cannot understand what is the formula with which it calculates distances, since euclidean distance is used only in PLANAR for projected data.

• If you are doing some analysis of "near distances", it would be more appropriate to get your data into a projected coordinate system first. Choose an equi-distant type. – Neil Ayres Feb 12 '15 at 12:44
• @Neil Could you explain the sense in which you mean "more appropriate"? On the face of it, geodesic distances are the correct distances and using a projection only creates distortions. In particular, an equidistant projection would be one of the poorest possible choices unless all points were close to the origin of that projection. – whuber Feb 12 '15 at 17:33
• Marika, do you want to know the fully accurate formula for ellipsoids or the approximate formula for a spheroid? The latter is explained in many threads here: search our site for haversine. For implementing a nearest-feature calculation even that's barely a start; the real issue is constructing an efficient algorithm rather than finding a mathematical formula for distance. (The tool would be worthlessly slow if it had to compute all possible distances between points and feature vertices/segments.) – whuber Feb 12 '15 at 17:35
• You should address this question to ESRI. Their software is closed, thus no one outside the company can know for sure. – Luís de Sousa Feb 17 '15 at 7:48