OpenStreetMap
I've uploaded some traces of my wandering around the new Tesco (and associated road and footpath modifications!) in Newtown. This is near where the old livestock market used to be (near the junction of Pool Road and Kerry Road).
This is new enough that it does not appear to be represented in any of the other online maps or aerial photography.
Now to edit the map (once I've read all of the documentation!).
Discussion
Comment from compdude on 6 January 2011 at 00:36
Don't copy from other maps (ie Google Maps,etc)! This is illegal, but a lot of people still get away with it.
Comment from LivingWithDragons on 6 January 2011 at 01:45
But if you have uploaded gps traces, they are ideal for using to get the line of roads. Combine them with your own notes or good memory.
Reading the whole 'documentation' is a bit hard to think about. We're not a great community at writing it and there ends up being various pages on the wiki to say the same things in a different order. You might also get into some confusing technical documentation for developers.
So I suggest reading enough till you feel confident you can do a few things you want, and give it a try. If you hover over the 'edit' tab you get some options, Potlatch 2 is a good option for beginners (or download JOSM if you don't like flash). In Potlatch 2, nothing is saved until you click the Save button, so if you mess something up then go back to the 'view' tab and don't worry about it.
Once you have made some edits, you could write another diary entry about it or ask on the IRC chat and someone should be happy to check it for you! Though are documentation is rubbish at being a good guide, there are lots of people happy to answer questions and help you out. Especially for people in Wales, we need more mappers there!
Comment from dekarl on 6 January 2011 at 13:16
You can attach the place you are talking about to your diary entry. OSM is about maps after all. :)
Comment from marscot on 6 January 2011 at 15:18
yeah have shot at drawing the road in, then add the shop and tag it with a name and any other info you have.
Comment from mannequinZOD on 6 January 2011 at 15:36
there is also lots to draw from Bing Imagery. I drew some roads in in the area, but I don't know any of the names. Have a go.
osm.org/edit?editor=potlatch2&lat=52.51649&lon=-3.30927&zoom=17