# Calculating distance to points on a coastline from all cells in extent

I'm on ArcMap 10.4.0.5524

Layers:

Layer 1: I have an outline (polygon) of an irregularly shaped island approximately 10km square in size. Layer 2: I have a layer with various points snapped to the island polygon representing locations I want to calculate distance to, let's call them coastal towns. Layer 3: I have the points layer (Layer 2) converted to raster. The extent of this layer has been changed to be the extent of a different layer approximately 200km square, which is all considered open sea. When I change NoData to be shown as a colour, this extent is displayed correctly. But when I zoom to layer, it zooms to where the coastal towns are instead of the extent of the whole layer.

The problem: I want to calculate the distance to the nearest coastal town from all grid cells in the 'sea'. I've tried to do this using the Euclidean Distance tool, which is probably the wrong one. What I get as output is a distance raster showing distances within the square expressed by the coastal towns furthest to the north, east, south and west, including areas on both 'sea' and 'land'. The maximum distance value returned is 2.56, which isn't correct and I want the values in kilometres.

How do I generate a distance raster using only routes available by sea (not crossing land, so I can't go with this and mask the result!), with results in kilometres and for the full 200km extent around the island instead of just the extent of the coastal town points?

• Have a look at the cost distance analysis tools and the path distance analysis tools in the spatial analysis toolbox. – GBG Jun 6 '17 at 16:04