Labels on OFM Charts

Labels on our Charts

It is quite difficult to get the labelling right on maps. Each label takes up some space and sometimes even obscures some information underneath, but obviously the maps must have labels to give important data, such as radio frequencies or upper and lower limits to an airspace. In general, we at the OFM would like to apply a consistent approach to labels on our maps in all countries, and this means that we frequently have discussions about what should be included in the label and even if a label is appropriate.

For instance, we are sometimes asked to show elevations and runway data in the aerodrome label. We have decided that this information is best presented in a table in the corner of the map, since it is unusual for a pilot to want to consult this data during flight, and so it is acceptable to have this data in a table. Also we have been asked to provide labels showing the names of small towns, but in this case we have decided not to provide these labels because we consider that the label would not help the pilot, since there is no good way of identifying which town is being referred to from the air. We had quite a lot of discussion about showing the height of mountains or indicating mountain passes on the map. Should we show the height of all mountains, or only the highest ones in a region, and should the mountain pass indicate a suggested trajectory? With respect to the last two questions we can see that it depends on each case, and as a result we have decided to leave it up to the contributor, who is the person who knows his region best. As a result, there is now a feature which allows originating contributors to input the heights of mountains and mountain passes, indicating the trajectory if appropriate. Currently it is the contributor who decides whether to include a label on the border of an airspace, and where to position the label, but in order to make contributing as simple and easy as possible, we are developing some software to automatically make the decision about including a label and positioning it, depending on the shape of the airspace and the clutter of information in the area. Another subject that has given rise to some discussion is the MORA data (indicating the minimum off route altitude that can be flown without worrying about the height of the terrain). Firstly, we have adopted an almost universal code which shows this data for areas which represent every half degree of latitude and longitude, and which present two numbers, one larger than the other, the larger indicating thousands of feet and the smaller one indicating hundreds of feet. Next we have decided to adapt the opaqueness of these numbers to their values, on the basis that it is more relevant to have this data displayed on map in a mountainous area than on a flat lower region, so that a value of over 10,000 feet appears almost in black, whereas 3,000 feet is shown in a very light grey colour. Another decision that has been adopted is to not show small streets, because we believe this merely causes clutter on the map, while not providing any practical benefit. But significant roads such as motorways or major trunk roads are shown, as are railways, because these can normally be easily seen from the air. We try to clearly show all forests, since we consider this is important for the pilot. However, we do not believe it is relevant to show obstacles on the standard VFR map with a 1:500,000 scale. In this regard the OFM maps are different from some other maps commercially available, but obstacles will be the subject of another complete discussion, since we are finalizing the system to input and maintain a very extensive database of obstacles.

We do apply a general rule, and that is that aeronautical information always has priority of space over general geographical data on the map.

Robert Nisbet