1:50 000 Scale Colour Raster Product Guide

This document contains additional theoretical information related to 1:50 000 Scale Colour Raster. All users will find the Product Information document useful and informative.

1:50 000 Scale Colour Raster is a data product similar to the popular OS Landranger Map series, showing a detailed overview of the landscape. It is a mid-scale product that's ideal for navigation. 1:50 000 Scale Colour Raster can be used to contextualise your data or as a map in its own right. It is aimed at recreational as well as businesses users, providing them with an excellent overview of the main features and communication routes across Great Britain.

The 1:50 000 Scale Colour Raster product provides a grid of easy to consume TIFF images. This grid is aligned to the National Grid (EPSG: 27700). The 254 dots per inch resolution has been chosen as it maintains the necessary clarity for text shown on the map.

Screen images can be plotted to produce a high-quality map. An example of the data is shown in the image below.

An extract of 1:50 000 Scale Colour Raster over part of Southampton, England.

Key features of the product

The key features of the product are as follows:

• Regular revision cycles, giving product consistency.

• Highly detailed mapping, showing airports, farms, hills, woodlands and commons, among other places.

• Easy to download and apply TIFF formats.

Product applications

1:50 000 Scale Colour Raster is aimed at recreational and business users and its graphic specification can help with the following:

• Development and land-use planning

• Environmental impact analysis

• Vehicle routing

• Asset management

• Marketing analysis

• Display and promotion tasks

Georeferencing

Georeferencing is not required when using the GeoTIFF file format as the tiles have already been embedded with georeferencing information.

To be able to view each TIFF tile in correct geographic relation to the National Grid and to other tiles, the tiles must be georeferenced. Geographic information systems (GIS) typically provide georeferencing as part of their functionality, but for each set of tiles, it is necessary to provide information on how the tiles should be ordered.

Ordnance Survey provides this information in a set of georeferencing files, also known as world files. A complete set of georeferencing files for 1:50 000 Scale Colour Raster is available to download free of charge from the Georeferencing files and land and sea tiles page of the OS website.

There are several different types of world file. Prior to downloading one of the sets, customers are advised to check with their system suppliers to find out which type of world file their system supports.

The conventions behind the files’ creation can be found in the product's technical specification. By using the conventions outlined there, this means that other datasets using the same conventions can be imported into the same GIS to add value to the raster map; for example, overlaying a routing or logistics network over the map or displaying a customer’s demographic information.

The georeferencing files should be saved in the same directory as the files of the map tiles themselves.

Data measures

Ordnance Survey measures the data in its products in one or more of the ways set out in the definitions of data measures table below:

Data measure	Definition	Sub-measure	Definition
Completeness	Presence and absence of features against the specified data content*	Omission	Features representing objects that conform to the specified data content but are not present in the data
Commission	Features representing objects that do not conform to the specified data content but are present in the data
Logical consistency	Degree of adherence to logical rules of data structure, attribution and relationships	Conceptual consistency	How closely the data follows the conceptual rules (or model)
Domain consistency	How closely the data values in the dataset match the range of values in the dataset specification
Format consistency	The physical structure (syntax): how closely the data stored and delivered fits the database schema and agreed supply formats
Topological consistency	The explicit topological references between features (connectivity) – according to specification
Positional accuracy	Accuracy of the position of features	Absolute accuracy	How closely the coordinates of a point in the dataset agree with the coordinates of the same point on the ground (in the British National Grid reference system)
Relative accuracy	Positional consistency of a data point or feature in relation to other local data points or features within the same or another reference dataset
Geometric fidelity	The ‘trueness’ of features to the shapes and alignments of the objects they represent*
Temporal accuracy	Accuracy of temporal attributes and temporal relationships of features	Temporal consistency	How well-ordered events are recorded in the dataset (life cycles)
Temporal validity (currency)	Validity of data with respect to time: the amount of real-world change that has been incorporated in the dataset that is scheduled for capture under current specifications
Thematic accuracy (attribute accuracy)	Classification of features and their attributes	Classification correctness	How accurately the attributes within the dataset record the information about objects*

*When testing the data according to the dataset specification against the ‘real world’ or reference dataset.