OK, thanks - so just "20" in OFFSETA will mean 20m.
In terms of the degree thing, I got it from Layer Properties but I wasn't sure if it was relevant or not (so, Angular unit =/= Vertical unit). Sorry, still new to the program!
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Speaking of which - how do I then use this viewshed to create a fuzzy viewshed? I've tried to follow the explanations on this forum but I'm a bit stumped as to which rasters I need to use.
I have:
750prj = A DEM Raster of the terrain for my study area
10km = A circular polygon representing the area within which I want to investigate visibility
ChurchTower = A point 20 m high from which I want to estimate the viewshed of "750prj" within "10km"
ChurchView = A binary viewshed generated from "ChurchTower" + "750prj"
I know the next step is to create a Distance Decay Buffer using the Euclidean Distance Function in Spatial Analyst but I'm not sure what files to use at what stages. I've read through the explanations online but I can't really get my head around it. When I use 750prj or ChurchView as the source raster, the output raster is entirely black, and when I use the ChurchTower point as the input I get an error and it won't generate at all.
Is there some way I should turn the ChurchTower point into a raster?
The ultimate goal of this is to create a fuzzy viewshed which represents visibility fading with distance from the centre point.
Thanks again for all your help.