Map Content
Those responsible for initially responding to emergencies require base-maps of a region as soon as possible. EXPRESSMaps supplies maps at a scale of 1:50,000, chosen to match the inherent accuracy of the source data and the current accuracy of GPS receivers (e.g. Figure 1). This universal scale means maps can be used reliably on the ground and have a footprint of roughly 600 square kilometres, depending on the latitude of the requested area. Map content has to cater for a range of uses, e.g. by field teams, crisis-management units, humanitarian aid organisations, logistics companies and security players. Content is a trade-off between two key constraints: source data and timeliness.

Source Data
The geometric accuracy of EXPRESSMaps depends entirely upon the source data. As of mid-2009, the coverage zone spans 100 million square kilometres, including more than 75% of the planet?s land surface (without USA and Canada). Areas close to the equator are not yet fully covered, due to the almost continual presence of cloud. Also not yet covered are the USA, Canada, UK and northern Europe, but accurate maps are available. Asia will be mapped within the next few months.
The area covered by the service corresponds to off-the-shelf orthorectified Reference3D [website 1] and SPOTMaps [website 2] satellite imagery from Spot Image. Reference3D and SPOTMaps data are reliable and have been evaluated and validated by numerous domain experts. Reference3D combines a Digital Elevation Model, a 5-m resolution ortho-image in black & white, and other quality information. SPOTMap is an ortho-image in natural colour at 2.5m resolution; both are based on SPOT5.

Rapid Mapping
The second constraint relates to ensuring map production within six hours of receiving a request. An innovative feature of the service is that the entire map production process is patented. Each step is optimised and timed to ensure prompt delivery under all circumstances, whatever the area of interest, whenever a disaster or emergency occurs.

Detailed Specs
Each map meets the same specifications and requirements, whatever the region or delivery deadline:

• absolute vertical accuracy: 10m CE90 (i.e. for 90% of the data) for slopes < 20°

• absolute horizontal accuracy: 15m CE90

• contour spacing: 50m

• scale: 1:50,000 (for files intended for printing)

• projection: UTM WGS84

• geographic and UTM coordinates
  product footprint: 15' x 15' between latitudes 50°S and 50°N; 15' x 30' between 50'70°S and 50'70°N.

Each map delivery (e.g. Figure 2) comprises a set of files which are compatible with a range of programs, including any GIS tool on the market, any freeware viewer, Google Earth and web-based services through a geoserver.

Operational Legend
Map content is easily interpreted due to a legend designed to fit production constraints. The theme and technical specifications are determined to a large extent by how the map will be used in the field. The information highlighted on each is chosen to help people and teams on the ground find their way around as easily as possible.

Transportation
The ground transportation network is the first layer of information entered. This is one of the map elements to receive most attention during the data extraction process. Two categories of roads or tracks are mapped: main routes and others. The distinction between the two is not based on technical criteria (road surface, number of lanes etc), but rather on their relative importance as a line of communication. The widest and most-used routes, and those linking the largest villages or towns, are classified as main routes. All others, from tracks to secondary roads, are classified as other routes. This unusual classification scheme is dictated by the need to extract information very quickly, and by the fact that mapped landscapes and road network density may vary enormously. For example, if all tarmac roads were classified as main routes and all other roads as other routes, some maps would only show one category and therefore be of limited use. Likewise, this scheme is adapted to the many territories where the main routes are in fact dirt tracks. The EXPRESSMaps classification is therefore functional, highlighting main routes to help teams reach their destination as quickly and easily as possible.

Other Features
Populated areas also receive special attention. The population layer comprises five classes, three of which are reserved for types of housing. Classes are distinguished according to housing density. Two additional classes cover industrial or trading zones in built-up areas. Large areas are represented by polygons, while points enable large buildings such as warehouses and factories to be quickly identified. Such landmarks are useful for navigation.

The remaining information on the maps results from trade-offs between source data characteristics, the level of detail expected at the chosen scale (1:50,000) and production time constraints. For example, land occupancy in other areas is rendered by ten additional classes. Many point features such as bridges, dams, airports and ports are also mapped, to facilitate operational use on the ground. Topography is represented by contours with a spacing of 50 metres, and by shading. High and low points (roughly eighty on each map) extracted from the DEM are also shown. Such information relating to terrain topography allows better and faster progress in the field.

Concluding Remarks
EXPRESSMaps (Figure 3) establishes a set of specifications and production procedures applicable to all the world?s landscapes. Its capability to supply users with 1:50,000 maps of almost any point on the globe in under a day is a revolution in map production. Specific resources for communicating with customers shorten the process and smooth the workflow to ensure map production in record time: a dedicated website [website 3] allows a user to open an account with a few clicks, pre-pay for maps with a one-year MapPass and select maps to meet their needs through a specially designed interface.

Acknowledgements
Thanks to Marc Bernard and Myriam Chikhi from Spot Image SA for help in designing the service EXPRESSMaps.