Sunday, 2 May 2010

OS VectorMap District

Using the experience gained with the OS BoundaryLine data I thought I'd take a look at the VectorMap District data that the Ordnance Survey have just released. It is organised into chunks based, not surprisingly, on the OS grid. The grid has 100km squares labelled with letters (you can give a grid ref without the letters, but the VectorMap uses the letters). Within each square there is a simple grid system with two parts, known as northings and eastings. The VectorMap uses a single digit of each to define a 10km square. When you have worked out which square you want and opened the folder for that square there is a variety of shape files in it. My village happens to not only fall across two 10km squares but two 100km squares, so I need SE92 and TA02 to cover the whole village.

The shape files cover a range of features: administrative boundaries, community services, heights, natural features by area and line, railway lines and points, roads as lines, settlements by area and line, text and tidal boundaries. I haven't investigated any of these exhaustively and some only cursorily and my findings so far are mixed.

The administrative boundaries seem to be the some of the same ones in the BoundaryLine dataset, but with the disadvantage that they are spread over many 10km tiles, so using the BoundaryLine ones is easier and has more boundary types.

Community services seem to be schools, I haven't found anything else. I might have expected all public buildings, for example libraries, which get highlighted on the StreetView rasters, but not as far as I can see. They are only shown as a point and with no name or other description.

Heights seem to be spot heights. The feature description is 'Heighted Point', which is neither descriptive nor English.

The natural features is interesting. It seems to contain woodland and water features, both seem useful. It also contains 'custom landform' which I still haven't identified yet. On tidal waters it seems to show the low-tide level, i.e. areas that always have water cover.

Railway lines shows the railway lines! It seems to show at least some sidings and multiple track sections. Some are labelled as multi track railway, some as single track railway.

Railway points shows stations with their names.

Road_line has the roads in the 10km square. They are listed with their type (A road, B road, Minor road, Local street - there may others elsewhere). The A and B roads have numbers, some roads have names, but most do not, including residential and minor roads, which would be the most useful. When I looked closely at the Road_line detail it was clear that some newer roads were missing, including a local estate built about ten years old. Also most private roads are missing too. In contrast, a small estate completed only about 18 months ago is in the Roads_line data. I would not trust this to be complete, and the lack of names limits its value.

Settlements by area seems to attempt to show where buildings are. It is showing this by blocking in areas, but these seem very arbituary. There are gaps between the blocks that don't really make much sense. It is more up-to-date than the Road_line data, since the estates that are missing from the Road_lines are present in the Settlement_area, including leaving the space for the missing roads. It does distinguish some building types, such as glasshouses.

Settlement_line seem to show electricity transmission lines, though not any more detail like their voltage, nor the position of the posts or towers.

Text is a list of points with the text that should be written there. The font size and display angle is listed too. The list of named items includes, places, waterway names, farms, bridges, in fact all sorts of things which may be useful to see on a map. Without the context of the object it seems useless to me.

Tidal_boundaries show the high and low water lines in some detail. I need to compare this to the high water mark in the BoundaryLine data, which I think is somewhat out-of-date. I'll post those results later.

Over all there is some interesting data in here, but, like the rest of the OS data, it is a mixed bag. I think OS have released a lot of data in a fragmented way that makes it hard to use without a lot of work to glue it all together. OSM seems like the perfect platform to put the useful data into, but only with quite some effort and, as always, best tempered with local knowledge.

1 comment:

Neeta said...

Community Services includes airports, 'education' (schools and universities maybe?), hospitals, leisure/sports centres and police stations.