In order to be able to smooth the road/rail ways for presentation at country level, I need to concatenate the individual segments into longer runs, and only then smooth. The task for tomorrow.

Downloaded the osm xml file for all France, folded new nodes into ‘array’ of lat and lon doubles, converted osm ways of roads and railways into GMT polylines and passed through GMT to create postscript map. This first attempt is far too finely grained with over 90,000 ways .. the ps file is 6.5Mb which is great for zooming in to look at fine detail, but very slow for the redraw. Need to find some smoothing software. Mapshaper?

Took my first osm xml file download yesterday – rhone-alpes.osm from CloudMade, 52m lines in 3.95Gb (uncompressed) so hardly planet.osm. Even so the parsing program needs large file support “cc -D_FILE_OFFSET_BITS=64”

First steps taken to parse out the node lat&lon pairs into array of doubles. Highest node id in rhone-alpes is 1.543.458.302 = 1.54Gnodes. Assuming this is not outrageously different from the number of nodes in planet.osm, we could store the lat&lon pairs for the planet in ~25Gb (2x8 bytes x 1.5Gnodes). That’s definitely do-able.

17m nodes of rhone-alpes loaded in 62 seconds on bog-standard laptop, so ~1.5hrs for the planet?