Guidance Notes for 1:250,000 Colour Raster

• All products
• 1:250,000 Colour Raster overview
• Download User Guide and PDF Legend

• Introduction
• Data Format
• Downloading the Data

Introduction

This product is currently only available to view as a map online. More details will be available when it is available to download. If you need more information please see the User Guide: Download User Guide and PDF Legend

The 1:250,000 Colour Raster images mirror the Ordnance Survey Road Atlas maps.

Data Format

1:250,000 Colour Raster data, as its name suggests, is a raster dataset. The 1:250,000 Colour Raster data is image data and so individual features cannot be removed from the dataset. Each tile covers 100km x 100km and there are 56 edge-matched tiles which cover Great Britain. This includes the Isle of Man.

Digimap delivers the 1:250,000 Colour Raster data tiles as compressed TIF (Tagged Image File Format) files. These are 256 colour 8-bit LZW compressed TIFs. Each tile is accompanied by a TIF World File, with the extension .tfw.

The .tfw file (TIF World Files), contains information that can be used by some Geographical Information Systems (GIS) to georeference the corresponding TIF image associated with the .tfw file. This information is important when combining the 1:250,000 Colour Raster image data with data from other sources. The .tfw files supplied by Digimap are sourced from the Ordnance Survey.

The .tfw file will look something like this:

25.000000000000000
0.000000000000000
0.000000000000000
-25.000000000000000
500012.500000000000000
199987.500000000000000

In order to make use of the .tfw file most GIS packages will require the .tfw to have the same filename as the TIF file it references. It should also be located in the same directory as the source file. e.g. tq.tfw provides the georeferencing information for tq.tif

The TFW file is a simple 6 line ASCII file. The table below explains what each line of information represents.

Downloading the Data

The data is available to download from the Data Download facility in Digimap in 100km2 tiles.