When making a map, there are a number of compulsory features that need to appear. They are:

• the north arrow * the scale in metric system. It is the international standard in sciences, it has to be used. No scale in miles or in any other non-metric system. * a clear legend of the symbols used in the map * a clear title that explicitly says what the map is about. This title can either be within the map's frame if there is room for it, or above the map's frame if the map takes all the space in the frame - which is often the case for maps showing terrain background, for example.

Below the map's frame, lined on the left, the following notices have to appear:

• year of creation of the map * the copyright symbol © * the relevant [VCP] logo * the relevant [VCP] Digital Map Library” * the relevant [VCP] url * the map's VCP ID (this ID is in the format ID##, where # is a number)

year © logo [VCP] Digital Map Library (http://www.virtualcities.fr *[VCP]-ID: M##)

When you create a map, three parameters count: the size of the map, its resolution, and its format.

As for the size, it depends on the type of media the map is intended to. Most of the time maps are intended to be printed on sheets or books that are roughly the size of an A4 sheet . This means that usually the width of a map is roughly 19 cm or 7.5 inches for a portrait printing, or roughly 27 cm or 10.6 inches for a landscape printing. Then there is no rules as for the proportions between the width and the height, it all depends on the map and what you want to show. Sometime maps can be intended for poster printings. Then there is no rule as for the size. Finally, maps can be intended for digital publication. Then, it is recommended to design the map to fit in an A4 sheet, as explained above, to allow people to use it in articles and other publications.

As for the resolution, it depends on the content of your map. The general rule is to be able to zoom in on the details without seeing pixels. Maps that contain only vector graphics (like map showing the political boundaries between several countries) don't need to be produced at a very high resolution. The average good resolution for vector maps is 150ppi. Maps that contain raster imagery, such as elevation background, must be produced at higher resolutions. It will depend on the quality of you raster datasets. The minimum resolution to get a decent image is 300ppi. The recommended resolution is between 500 and 600ppi. Then, resolutions can be a lot higher, it all depends on the quality of the datasets used, and on how much you want people to be able to zoom in.

Finally, as for the format, there is only one rule: all maps have to be exported as TIFFs. From them we can convert them into jpegs for internet uses. But it's important to have original TIFFs for archival pruposes, and to meet the possible needs of tomorrow's technologies.