Frequently Asked Questions

What is administrative geography?

Administrative geography concerns itself with the hierarchy of areas relating to national and local government in the UK. Examples of administrative boundaries are wards, local authorities, counties, parliamentary constituencies and clinical commissioning groups. These were used as a basis by the UK Census offices to break down into Output Areas and Super Output Areas. Adminstrative geography is particularly useful to the public and health sectors.

The table shows that super output areas and wards are made up of output areas. Local authorities are made up of wards and counties are made up of local authorities.

Both clinical commissioning groups and parliamentary constituencies are made up of output areas.

Output Area < Super Output Area < Local Authority < County
Output Area < Ward < Local Authority < County
Output Area < Clinical Commissioning Group

Output Area < Parliamentary Constituency


Boundaries Example Number of that
boundary in the UK
Average number of households
within that boundary
Output Areas E00067800 223,060 110
Super Output Areas E01013428 41,773 590
Wards E05010327 (Rawcliffe & Clifton Without) 10,604 2,322
Local Authorities E06000014 (York) 434 56,745
Counties E10000023 (North Yorkshire) 142 173,431
Parliamentary Constituencies E14001062 (York Outer) 646 38,123
Clinical Commissioning Groups (England only) E38000188 (NHS Vale of York) 211 337,906


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What is a crow fly distance?

A crow fly distance is simply the shortest distance (e.g. in miles) from one location to another. It doesn’t take into account the method of travel (e.g. type of vehicle or roads) between these locations.

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What is a drive time matrix?

The TimeTravel drive time matrix calculates times and distances between pairs of postcode sectors (e.g. LS12 1) or pairs of postcode districts (e.g. LS12) for all postcode areas in Britain and Northern Ireland.

Both the time and the distance are calculated for the quickest journey between locations. The shortest journey is usually of much less interest.

The quickest journey is based on the Collins Bartholomew road network. Each road link is classified into several road types and as an added refinement the urban density of each road link is used so that a minor road in Birmingham drives much slower that a minor road in a rural area or village.

We assign an average speed to each type of road link based on Collins Bartholomew measurements outside London, and Department of Transport figures inside London. The database can be calculated using different speed tables. The standard product uses off-peak speeds. This tends to give optimistic times because no journey stoppages, road works, etc can be taken into account. To model them afterwards a constant factor could be used.

Because postcode sectors and districts cover an area there has to be a measure for averaging the source to target values. Some postcode sectors can be several miles or minutes across so the minimum and maximum figures between any two points could be quite different. TimeTravel calculates using the source centroid (a point near the centre) and visits all the junctions in the target area. These are then averaged to get the time and distance. Because densely populated areas have a higher density of junctions, this tends to weight the result to the most useful value.

Because there are over 9,000 postcode sectors in the UK, the database contains over 80,000,000 records. The database repeats A->B and B->A records. This makes searching easier and occasionally the values can be very slightly different.

TimeTravel is updated when new releases of postcode information become available, between two and four times a year and incorporate the latest road network available from Collins Bartholomew

Large-user sectors (sectors assigned by Royal Mail to business users) have been added as sources and targets. Where a large-user sector has a residential equivalent, times to and from that equivalent have been used.

Latest features:

  • Road links passing over bridges have been classified separately and assigned low speed values
  • Links inside the London congestion zone have been classified separately and assigned low speed values to model reluctance to enter
  • The speed tables used have been revised based on Department of Transport research figures. This generally results in longer times
  • Ferry routes have been modelled to enable drives from every sector to every other sector

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What is Enhanced Metafile?

The EMF format is the 32-bit version of the original Windows Metafile (WMF) format. The EMF format was created to solve the deficiencies of the WMF format in printing graphics from sophisticated graphics programs. The EMF format is device-independent. This means that the dimensions of a graphic are maintained on the printed copy regardless of the resolution in dots per inch of the printer. In a network, the smaller file size of the EMF format reduces network traffic. EMF is the spool file used by the Windows operating system.

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What are MapInfo (Mid/Mif) and ESRI Shape formats?

Mid/Mif (the MapInfo Interchange Format) and ESRI Shape (also known as Shapefile) are two of the most commonly used geographic formats and are well supported by almost every GIS product, including Prospex.

A Mid/Mif file physically consists of two files: a .mif which contains the geometry and a .mid which contains the attribute data.

Shapefiles spatially describe points, which could for example, represent water wells, lakes and rivers respectively. Each item may also have attributes that describe the items, such as the name. A Shapefile physically consists of several files. The most important ones are:

  • .shp contains the actual geometry
  • .dbf containing the attributes
  • .shx containing the link between the .shp and the .dbf

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What is GIF?

GIF (Graphics Interchange Format)

A file format that is used widely on the internet due to its wide support and portability. The format supports animations and allows a separate palette of 256 colours for each frame. The colour limitation makes the GIF format unsuitable for reproducing colour photographs and other images with continuous colour, but it is well-suited for more simple images such as graphics or logos with solid areas of colour.

GIF images are compressed in a lossless fashion (i.e. all image information is restored when the file is decompressed during viewing) to reduce the file size without degrading the visual quality.

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What is JPG or JPEG?

Joint Photographic Experts Group (JPEG, JPG)

A JPEG (pronounced JAY-peg) is a graphic image file created by choosing from a range of compression qualities such that you can make a trade-off between image quality and file size. JPEG is "lossy," meaning that the decompressed image isn't quite the same as the one you started with. (There are lossless image compression algorithms, but JPEG achieves much greater compression than is possible with lossless methods.)

Together with the Graphics Interchange Format (GIF) and Portable Network Graphic (PNG) file formats, the JPEG is one of the image file formats supported on the internet, usually with the file suffix of ".jpg".

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What is PNG?

Portable Network Graphic (PNG)

A PNG (pronounced “ping”) is a file format for image compression that, in time, is expected to replace the Graphics Interchange Format (GIF) that is widely used on today's internet. Like a GIF, a PNG file is compressed in a lossless fashion (meaning all image information is restored when the file is decompressed during viewing). A PNG file is not intended to replace the JPEG format, which is "lossy" but lets the creator make a trade-off between file size and image quality when the image is compressed. Typically, an image in a PNG file can be 10% to 30% more compressed than in a GIF format.

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What is Windows Metafile?

A WMF file contains a sequence of graphical-device-interface (GDI) function calls ("commands" to the Windows operating system) that results in the presentation of a graphic image. Some of the function calls are equivalent to vector graphics statements and others identify stored bitmap or literal specifications of which bits to illuminate (raster graphics images).

Using WMF files rather than already-built bitmaps saves space when many bitmaps are used repeatedly by different components of the operating system or of an application.

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What are VML and SVG files?

What are VML and SVG files?

VML (Vector Markup Language) is used to produce vector graphics. Microsoft implemented VML into Internet Explorer 5.0 and higher and in Microsoft Office 2000 and higher.

SVG (Scalable Vector Graphics) can be dynamic and interactive and allow three types of graphic objects:

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What is geocoding?

Geocoding is one of the key functions of a geographic information system (GIS) and is often applied to address lists. For example a company can geocode a list of their customers’ address in order to pinpoint them on a map or analyse their geographic distribution. This may reveal trends that the company would otherwise be unaware of, such as areas of particularly high or low customer density, which may suggest reasons for the successful recruitment of customers.

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What is the difference between vector and raster graphics?

A vector graphic is a graphic drawn as lines, polygons and text, whereas a raster graphic is drawn as an array of coloured dots. Raster graphics are faster to display but the image quality suffers when they are scaled up or down. They are usually larger than a vector graphics image file and are supported by a larger number of applications.

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What are map scales?

For a map to be of a useable size the information must be shown proportionately smaller than it actually is. This proportion is the "map scale", which shows the relationship between distances on the map and distances in the 'real world'.

Map scales are usually given as a ratio, e.g. 1:100,000. In this scale, one unit of measurement on the map represents 100,000 of the same unit of measurement on the ground. The first number is always '1' and the second number is different for each scale. "Large is small" or the larger the second number the smaller the scale (detail) of the map.

Most geographical areas have been mapped at different scales. When choosing a map, its intended use should be considered before deciding on which scale to use. For a close view that will give you the most detailed information of a small geographical area, choose a map with a small second number, i.e. 1:100. For a broad general view of a large geographical area you would use a map with a larger second number, i.e. 1:100.000.

Scale 1 inch on the
map represents:
1 centimetre on
the map represents:
1:10,000 (large scale) 833.5 feet 100 metres
1:25,000 (large scale) 2,083 feet 250 metres
1:50,000 (large scale) 4,166 feet 500 metres
1:100,000 (mid scale) 1.6 miles 1 kilometre
1:250,000 (mid scale) 4 miles 2.5 kilometres
1:500,000 (mid scale) 8 miles 5 kilometres
1:800,000 (small scale) 12.8 miles 8 kilometres
1:1,000,000 (small scale) 16 miles 10 kilometres


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What are Output Areas?

Output Areas (OAs) were built from clusters of adjacent unit postcodes as at Census Day 2001. They were designed to have similar population sizes and be as socially homogenous as possible (based on tenure of household and dwelling type). Most OAs consist of entirely urban postcodes or entirely rural postcodes, avoiding urban/rural mixes where possible.

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What is postcode geography?

Postcode geography in the UK is a nested, hierarchical structure as illustrated below.

Postcode: Every address in the UK has a postcode (e.g. YO23 2UE) which is shared between approximately 15 properties.

Postcode sector: All addresses sharing the same sector code (e.g. YO23 2) fill a geographic area that can be defined by a postcode sector boundary.

Postcode district: All postcode sectors with the same district code (e.g. YO23) can be grouped to form a postcode district boundary.

Postcode area: All postcode districts with the same area code (e.g. YO) can be grouped to form a postcode area boundary. Our mapping software, Prospex, enables you to analyse your markets in depth by combining several datasets with your own data. Postcodes provide the mechanism for linking together all the datasets you need to use. Postcode boundaries are the most commonly used building blocks for market analysis tasks.

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What is Social Marketing?

Although first coined in 1971, the term social marketing has only recently become a bit of a buzzword in the last few years. Crudely put, it is the application of commercial marketing techniques in social policy to elicit behavioural changes for the social good. Examples include encouraging seat-belt usage or discouraging people from smoking in public areas.

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What are Super Output Areas?

Super Output Areas (SOAs) are designed to improve the reporting of small area statistics. Before SOAs, the standard unit for presenting local statistical information was at electoral ward/division. However this had drawbacks as electoral wards/divisions vary greatly in size, which is not ideal for nationwide comparisons and they are subject to regular boundary changes, which creates problems when trying to compare datasets from different time periods.

It was therefore decided to build a range of areas of that would be a consistent size and whose boundaries would not change. These would be built from groups of the Output Areas used for the 2001 Census and would be known as Super Output Areas.

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