Ordnance Survey – Great Britain's national mapping agency
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6.4: Derived mapping (2)
Text placement
It is difficult to place text on a map so that it is both legible and clearly asso
ciated with the feature that it is annotating. Text placement refers to the complex challenge of achieving this in an efficient manner to generate high-quality results. Text can of course be placed by simple manual methods, although this is a time-consuming and inconsistent process. The automatic generation and placement of text can result in savings in time and labour together with a more repeatable result. Although seemingly simple in concept, this automatic process is remarkably difficult to achieve in practice and is the subject of widespread research interest.
The manner in which text is placed on a map depends largely upon the cartographic symbols that are chosen to represent the points, lines and polygons of the source data and how they relate to each other in a spatial context. One layer’s text or symbols may have a dramatic impact in determining the placement of another layer’s text. It is therefore necessary to assemble all the data layers required within the final map, then symbolise their features according to the map’s extent and scale before text placement takes place.
Modern automatic text placement software offers flexible placement options. There are now choices of font styles, sizes and colours; preferred location of a piece of text; weightings as to which text is more important and takes preference over other text (for example, road text might be more important than building text); and minimum and maximum allowable distances between different labels. A predetermined set of rules can therefore be created applying to any source data for any location at any given scale. This results in a map product that is generated more consistently and also more efficiently, thereby greatly reducing the amount of manual effort required in its production. See below for an example of automatically generated text.