Mapping with GIS: When seeing should not always mean believing. Mr Oliver Tomlinson Senior Lecturer in Geographical Sciences School of Education Health and Sciences

“…all maps must tell white lies. And sometimes these lies are not so little. Maps are informative, but they can also be deceptive, even threatening.” H.J. de Blij “Because of personal computers and electronic publishing, map users can now easily lie to themselves - and be unaware of it.” M. Monmonier

The problem is no longer limited to those who have always sought to deceive. GIS and mapping tools are now in everyday use by those without GIS, geographic or cartographic training. Even the ‘experts’ can get very different answers to the same questions using different GIS or different processes within the same GIS.

In the beginning… What data do we need to solve a given problem and at what level of detail? Limitations of humanistic perception? Issues with common GIS data sources,...e.g. maps maps Scale of map Cartographic generalisation (e.g. road widths) Hard boundaries (e.g. soil map) Currency of survey V date of publication

Data capture DigitisingDigitising is still a common form of data capture. the process is highly selective further spatial error is added to the data prone to operator bias (e.g. left V right hander) quality standards do exist Existing digital data spatial accuracynon GI scientists attribute accuracydo not question level of generalisationthese issues! fitness for use should always be the maxim

Spatial Representation (e.g. raster data) At what spatial resolution do we represent the World? What are potential implications of this choice? buildinglakeriver woodland Real WorldLow spatial resolutionHigher spatial resolution

GIS Analysis I (the black box of wonders) Many GIS users never question the way the tools they are using operate and are thus unaware of any implications. For example, the algorithm underpinning a given GIS operation may vary between different GI systems. This means it is possible to get two different (potentially very different) answers to the same question using the same data and methodological approach. This also applies in a single GIS when the operator is confronted with options / choices (use defaults?).

GIS Analysis II (hard versus soft approaches) Traditional GIS problem solving employs hard (yes/no) decision making. But this has issues. E.g. Find all steep slopes. But when does a slope become steep? Better approach is one that uses probability based on things like fuzzy set membership. Softer decisions, but more complex! Slope - degrees Probability of being steep

GIS Analysis III (seeing is believing?) The areas used as the basis for study can have a big impact on the results. Consider poverty. You could map it at National, Regional, County, District, Ward or Enumeration District level (and that’s just census areas). Apparent spatial patterns of poverty can appear and disappear depending on the areas used. This is termed MAUP - Modifiable Area Unit Problem. It stems from the use of arbitrary mapping units for the analysis of continuous phenomena.

Interpreting the results I The results of an analysis can look black and white. Burglary hotspots probation Big issues if used to determine practice / policy! Source: Derbyshire Constabulary, 2003.

Interpreting the results II The GIS display ‘defaults’ may not be appropriate and could be very misleading. An operator may choose display options which completely hide or over emphasise spatial patterns. Colour, symbol size, method of data classification, number of classes, data aggregation are all factors which are manipulated in the production of maps. GIS output - Maps are a form of social control! - they portray specific social and power relations - they serve their creators

In Summary GIS are very powerful tools which have become widely accessible. Few users however have the breadth of expertise required to use them correctly. Never accept a map produced by a GIS at face value. Question the data it is based on, question the way it has been processed and analysed, question the way it has been presented.

Mapping with GIS: When seeing should not always mean believing. Mr Oliver Tomlinson Senior Lecturer in Geographical Sciences School of Education Health and Sciences