I know Normangill well. It's situation just outside Crawford is a fascinating one, and one which appears to show a very detailed knowledge as far as river valleys, watersheds and connected through-routes go, back in the time of its construction.
It is not far (just a few miles) from the massive Meso/Neo settlement discovered here.
http://www.biggararchaeology.org.uk/news22_311010.shtml
And this wee video shows some of that excavation.
Later on, Normangill Henge (almost) acted as a roundabout for two main Roman Roads which met up near Crawford Roman fort. One route came up what is now the M74 corridor (from the Roman Camp at Little Clyde) and the other, the great upland branch of Roman Road, which connected the Nithsdale Roman network with Crawford fort via The Dalveen Pass.
Even today, Normangill Henge lies in a incredibly central position within Scotland's communications network. It sits a few hundred yards of the River Clyde (and its confluence with the Daer Water), next to the M74 Motorway, close by the main Glasgow -> England Railway Main Line, yards from the A702 which connects Edinburgh and South Lanarkshire to Dumfries and Galloway.
At Clyde Law just beyond Normangill Henge, are the sources of the three major rivers of Southern Scotland, the River Tweed (flows into the North Sea), the River Nith (flows to Solway Firth) and the River Clyde (flows to Firth of Clyde). They all rise from different sides of that same hill.
The siting of Normangill Henge was very carefully chosen!