Hi all, Thanks for all your help with this. Thought I should update.
After getting confirmation of the validity of using the data, my friend and his colleagues successfully merged their postcode list with the CodePoint Open dataset and sent me the results. I then converted the eastings/northings to lats/longs using a Python routine I found on the web [1] (having first tested it out in QGIS using random postcodes from CodePoint Open, of course!) and sent it back to my friend who loaded the data into OpenHeatMap. His boss was happy and my friend bought me a couple of pints, so all is well. A few things to throw out there: -- I'm now properly in awe of proper GIS users. I had no idea that coordinate systems were so numerous and so complicated. For example, OS themselves provide a stand-alone batch coordinate converter [2], and I first tried using that to do the job, but found that the results didn't match when loaded into QGIS. So I searched again and found the Python routine [2] which *did* match. Evidently I wasn't using the OS software correctly, but no idea why. -- OpenHeatMap doesn't do true heat maps (or not that I could see anyway). Its main use seems to be things like house-price variation, where you have a *value* associated with each datapoint, rather than being interested in the *density* of datapoints. However, you can colour the points so that their overlap creates the illusion of a heatmap, which is still pretty useful for amateur use such as this. I tried following the QGIS tutorial kindly linked to by Steven Horner [3] but although each individual step seemed to work, I couldn't get the same end results. -- On a different but tangentially-related note, I had a look at the OS contour data the other day, just for kicks. It's in a format that, whilst open-able by QGIS, bears no relation to any other data I have (e.g. BoundaryLine shapefiles). It uses a different co-ordinate system, and Googling the relevant terminology lead me to a series of articles that each left me more baffled than before. Again: tricky stuff, this GIS lark. Maybe I should stick to GPS uploads, POIs and Bing tracing ;-) Again, thanks all. David. [1] http://hannahfry.co.uk/2012/02/01/converting-british-national-grid-to-latitude-and-longitude-ii/ [2] http://www.ordnancesurvey.co.uk/oswebsite/support/os-net/grid-inquest.html [3] http://qgis.spatialthoughts.com/2012/07/tutorial-making-heatmaps-using-qgis-and.html
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