All map elements need to be legible, meaning that they are readable, understandable and recognisable. All need to be large enough and clear enough relative to the viewing scale and the media on which the final map will be displayed.
Legibility of most map features depends on colour and size which ultimately make them noticeable and recognisable. Symbols need to be simple enough to recognise and offer good contrast against the background.
Text can be made legible with a good choice of font, good colour contrast against the background, suitable font size, character spacing and the use of masks or halos. Like any other map feature text can also be made more recognisable by choosing a representative colour, for example, blue text is immediately recognised as being related to water.
The proximity of map elements to each other is also important to the overall legibility. Overlapping symbols and text should be avoided where possible in order to make the information clear to the user.
To achieve legibility a process of cartographic generalisation is often required - this can take many forms; from simplification to amalgamation and will be dependant on the scale and use of the map.
OS VectorMap District – this is the backdrop colour style raster version of the product which has a nominal viewing scale of 1:25,000.
We have chosen fonts based on their on-screen legibility and ensured that the various fonts work in harmony yet are still distinguishable from one another. Various text sizes and colours have been used to represent different groups of features logically, for example, the spot height label colour matches that of the corresponding point feature. We have set many rules and used a complex, automated labelling system to ensure that symbols and text don’t overlap. Halos have been applied to text and symbols so that they are clear and legible amongst the surrounding detail.
The colour palette ensures that all features are legible and outlines are used to increase the contrast of certain features. The map features have been generalised to ensure that they are legible at the recommended scales. Buildings, for example, have been amalgamated, simplified and those under a certain size have been omitted from built-up areas or enlarged if isolated.
Back to Cartographic design principles.