The importance of effective map design

Crucial to effective communication of spatial information is the use of suitable mapping techniques that convey results objectively.  Effective mapping requires both an understanding of the mapped phenomena as well as the mechanisms to present the data appropriately.  This is particularly true for any maps that display data related to epidemiological risk in order to avoid misinterpretation or to over or under-emphasise particular results, as the classic examples by Monmonier (1996) illustrate.

Mapping has become far easier with the development and adoption of GIS.  Nevertheless, although data visualisation is integral to all stages of GIS analysis, it is important to remember that data views and screen grabs are not maps and might best be described as working documents forming part of exploratory data analysis.  A map will usually be required to display results or to convey information to a third party and each will require a different approach to the design.  It is for this reason that cartographic skills are just as important in GIS as analytical ability in order to communicate effectively.  Every map should be individually designed, using cartographic principles which enable the creation of a product that works with human cognitive processes to create meaning.  Design should reflect both the needs of the audience and the intended purpose and should include all relevant aspects of spatial and attribute data organisation, symbolization, application of colour, typography, and design and layout.  This is as true for web-based maps as print maps though each brings with it different considerations (Kraak and Brown 2000).

Map design can be directed by ‘good practice’ and the following factors should always be considered as part of the process:

The purpose of the map: Who is the intended audience  (e.g. what is their experience with map use) and how much will they interact with the map (e.g. presenting results or exploring data).  There are numerous options for data display and the map purpose must be closely tied to an appropriate mapping technique (MacEachren and Kraak 1997, Kraak and Ormeling 2003).

Map controls: Who is the audience, what output media are you using, what is the viewing distance, what is the map scale? Is some generalisation/simplification required?  It is highly likely that manipulation of the map detail will be required to ensure it is fit for display at certain scales and for certain purposes.

Projection: Map projection distortions alter fundamental properties such as: area, distance, shape, direction, size, scale (Maher, 2010).  The choice of map projection will, therefore, be related to the map purpose and can have a fundamental impact upon how data are portrayed.  Ignoring the projection is a major fault of many maps and one that can ruin the message.

Variable representation: Map components need to be assigned meaning.  They usually co-notate a particular meaning such as bigger than, more than etc. Remember that all the features of a variable can be changed, including size, shape, spacing, orientation, hue, lightness (Dent et al. 2008).  Using effective representation depending on whether the data is nominal, ordinal, Interval or ratio.  The combination of data type and level of measurement will play an important part in how symbolisation is performed so it is both mathematically and cognitively appropriate (Bertin, 2010)

Classification: The choice of classification scheme will affect the displayed spatial pattern, particularly for the display of thematic data using choropleth mapping techniques.  Classification scheme choice should be an informed choice based on appreciation of available alternatives and of the overall message (Slocum et al, 2004).

Colour: Colour has meaning, and there are a number of colour conventions that should not be ignored as this will confuse the reader.  Additionally, colour use should be handled very carefully to ensure effective design.  Many GIS default colour choices are cartographically poor but alternatives exist to assist with more appropriate colour choices (Brewer, 2005; Brown and Feringa, 2003).  Remember that a significant proportion of the population is green-red colourblind, so avoid this colour combination where possible.

Typography: A number of different factors should be considered such as map purpose (i.e. what needs to be labelled), font size, type, style and case, letter spacing, curvature, orientation, resolving type of feature conflicts.  Typography on a map often receives little attention but it is vital to communicate meaning so users can understand the map. (Robinson et al. 1995).

Overall arrangement: Emphasise what is important on the map - e.g. use contrast and build a hierarchy.  Frame and balance the map, not the page.  Structure the figure and ground effectively using the overall space and, minimising wasted space on the map (Kraak and Ormeling, 2009). Consider any inclusions that will add to the effectiveness of the map such as insets, titles, scale, explanatory text copyright notice etc.

Legend: The legend is a crucial part of the map and needs careful design.  Readers should be able to clearly interpret variable meanings and the legend should add information (Brewer, 2005)

Maps are informative and persuasive tools.  They are especially useful for revealing spatial pattern in information, and thus highlighting inequalities and targeting hotspots.  Conversely, maps can be notoriously misleading; either intentionally or unintentionally they can lie.  Cartographic decision-making for effective mapping can be both time-consuming and complex.  Getting results is not the only goal of geographical analysis; communicating them is just as important and inappropriate cartography can negate effective analysis (Darkes and Spence, 2008).

 This page was written by: Linda Beale, Imperial College London