Wednesday, 23 March 2011

OS MasterMap background maps

OS MasterMap data is now available to download in a rasterised (image) format from Digimap's Data Download facility. If you need an image of OS MasterMap data (for example, as a backdrop map) but don't need the complexity of the original vector data, this new stuff is for you.

OS MasterMap – detailed but complex

OS MasterMap is the most detailed product offered by Ordnance Survey. Maps made with with OS MasterMap have been available through Digimap's mapping facilities since 2007, but if you wanted to use OS MasterMap as background for a customised map by overlaying your own data in a GIS you needed to download and convert the raw GML data. If all you want is a detailed colour background image, this seems like a significant investment of time.

Rasterised OS MasterMap - images not data

Digimap now offers OS MasterMap as .tif images at two scales: 1:1000 and 1:2000 through the usual Data Download facility. This saves you having to download, convert and import the data using specialist GIS software.


Where do I get the OS MasterMap raster background maps?

Log in to Digimap's OS Collection, go to Data Download and select which scale of OS MasterMap image you want from the list of products. The images are tiled in 1km square tiles, so you can select your area of interest, and the tiles covering it, in the same way as other tiled datasets.

The scales are determined according to the distance on the ground represented by each pixel. The larger scale images are based on a measurement of 0.3125m per pixel. The smaller scale images are based on a measurement of 0.625m per pixel. These equate to approximate scales of 1:1000 and 1:2000 respectively, although these are dependent on the screen resolution of your monitor. You can easily display the maps at other scales, but some loss of image quality may occur if you do.

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