Its one of those things when you’re tinkering with geeky stuff that sometimes something niggles at you – you know its probably quite easy but you can’t quite put your finger on how to achieve something the way you want it.
And then one day it finally becomes obvious, your hand makes contact with your forehead and you can move on. This is one of those moments.
Convex Hull – the GIS version of stretching a rubber band over pins in a map is easy – most GIS tools have a menu item to do that somewhere.
That’s great if you don’t have any inlets and concave edges to your outline – if you do you need a Concave Hull.
Concave Hulls – a GIS version of vacuum wrapping a set of points plotted on a map.
Sounds easy. Easy to do with a pencil and paper – its just dot-to-dot with the outer-most points – but not so obvious using mapping software, or at least for me anyway.
BUT I’ve finally figured it out (with the help of some very good web resources).
I use a combination of Qgis and PostGIS – brilliant open-source GIS tools. Assuming you have these and can install pgRouting as well then Concave Hulls are very easy indeed!