Guidance Notes for OS Street View®



Introduction

Ordnance Survey's OS Street View is street-level, backdrop map data that is specifically designed for online applications.

It provides a scanned image of street-level mapping that can be combined with other data in a geographical information system (GIS), enabling you to clearly visualise a wide range of information in a geographical context. The street-level detail of OS Street View makes it particularly useful for displaying specific localities.

For example, as a road planner, overlaying your own statistical data onto a backdrop of OS Street View enables you to instantly identify individual road junctions where a high number of accidents have been recorded, allowing traffic-calming measures to be targeted to high-risk areas.

Data Format

OS Street View is a raster dataset, and as such when viewed in online maps the features cannot be turned on or off.

Digimap delivers OS Street View as a compressed TIF (Tagged Image File Format) file. This is a 256 colour 8-bit LZW compressed TIF. The 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:

100.000000000000000
0.000000000000000
0.000000000000000
-100.000000000000000
50.000000000000000
1299950.000000000000000

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.

Line Explanation
1 X resolution: dimension of a pixel in the X direction
2 The magnitude of translation
3 The magnitude of rotation
4 Y resolution: the negative of the dimension of a pixel in the Y direction
5 The X ground coordinate of the upper left pixel
6 The Y ground coordinate of the upper left pixel