Mapping Hacks

i recall talking years ago to paul at state51 about creating a free grid system, a free national or international reference system.

the British National Grid, as defined by the Ordnance Survey, is a transverse mercator projection. The convenience of this projection is that units of it correspond to distances in metres. The Geography::NationalGrid module for perl talks about a grid:

Conceptually each object represents a point on the
ground, although you some grid systems may take that point to be a cor-
ner of a defined area. E.g. a 6-figure OS National Grid reference may
be thought of as the point at the south-west of a 100m by 100m square.

Tragically enough, as a city person who does not really visit the country i am not really familiar with the landranger-style larger-scale streetmaps; i am used to the bartholomews style streetmaps as in the A-Z, and A-Zs for other cities. I imagine people ‘read off’ the X and Y coordinates on their paper maps, and find this useful for bearings.

The A-Z has a different kind of grid system which works with its index, a street gazetteer contained in the back of the book, taking up almost half of it. Each street has one or more references to a page with a square - F4 or D6, etc. the letters run across the fold onto both pages.

With web mapping, we’ve rather lost the concept of pages, instead just having a pane, through which we can zoom and pan; the ‘godseye’ fantasy through a small window. When we can overlay markers and highlight features on screens, why do we need a grid system to help you reference between things in the map and things in the world?

A grid system does have other, more conceptual usefulness though. Looking at a map, and judging the length of a walk on a journey: “oh, it’s only three squares on the A-Z, that’s not too far”, or the constrained walk, north to south within one square of the A-Z grid.

I wonder what features an ideal grid would have, how its segments would be measured. Whether inventing another Transverse Mercator based grid system just like the National Grid would have any point. How we could reproject this putative grid system and extend it to other areas…

Posted in cartographic |

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