GIS Map Output Lecture Notes PDF

GIS Map Output Introduction to GIS Dr Lawal Billa Environmental and Geographical Sciences  Cartography The art and science of making maps (International Cartographic Association) Note –map production has a element of art... We can lea...

GIS Map Output Introduction to GIS Dr Lawal Billa Environmental and Geographical Sciences  Cartography The art and science of making maps (International Cartographic Association) Note –map production has a element of art... We can learn the principles but there are lots of subjective judgements Mapping is a process of abstraction – so good maps display abstract data clearly and quickly Think about the end user and their understanding of the abstraction proposed Your initial thought should be : The objective of the map: what to show or not to show Reality of the map: should it look real or as a diagrammatic representation? The scale : how much detail and accuracy is required The limits of the map making software: what are the mapping capability of the software The audience: who is it for and what is their background and the purpose for the map Making Maps: what you need to think about Map clarity Visual contrast Visual balance Relative size of figures and ground The map hierarchy (which entities on the map have the greatest importance?)  Mapping as Abstraction Impossible to represent whole of a complex world on a single map World complexity need to be broken into categories of information What information are abstracted? Most commonly think of Ordnance survey maps These are generally abstractions of physical entities (roads, rivers , building etc… They also include topographic and environmental information (eg. Contours and vegetation) Many other types of information we can abstract and display as a map……. Information for abstraction  Map Types Socio-economic map (employment) Cadastral Map ordnance survey streetwise (1:1250 mapping product) Vegetation Map Road Network Map Bathymetry Map (New Zealand) Light Pollution Map(United State) Spatio-temporal Maps (Australia) Change in assemblage of birds(Australia Antarctic division)  Base Map Most maps superimpose abstracted information on top of a relevant base map Base map usually identifies relevant boundaries for map user Allows the spatial context of information to be conveyed No base map = No value Map construction Some basic principles  Scale and Generalization It is impossible to map the complexity of the Earth as a scale representation Rule of thumb : large scale= more detail = less generalisation  Generalization Always involves loss of information Original essence of map should try to be preserved Try to maintain accuracy in : Topology Attributes General geometry- coarse shape, orientation etc. Visual hierarchy amongst mapped entities Map Components Essential map components Map output should have the following : Title (define what map is about) Ground (background) Grid (defining the spatial reference) North arrow (defines direction/orientation Legend (defines the semiotics Scale (provide map to ground measurement) Supplementary information (date production, data source etc…)  Semiotics (the study of symbols) Mapped data are displayed using graphical symbols The symbols display the Nominal, ordinal , interval or ratio measurements of the geographical phenomena of interest As with spatial data models, graphical symbols can be created from point , lines or polygons GIS are readly capable of producing and displaying symbols for maps To use these capabilities efficiently it is important to have basic knowledge of semiotics Semiotics: map variable Semiotics: map variable Introduction to GIS  Strategies for Semiotics Strategies for determining how to utilise range of graphical variable can be based on measurement levels Levels of measurement: Nominal Ordinal Interval Ratio  Nominal Data Nominal data does not imply hierarchy through the symbols. It simply and effectively assigns a different symbol for each category  Ordinal Data Ordinal chooses symbols to demonstrates hierarchy in the data (e.g. Line thickness to show road classification hierarchy)  Interval and ratio data Interval uses a continuous set of semiotics so each data point has unique symbols Ratio categorises data and apply nominal or ordinal symbols as appropriate  Summary Creating map output is a mixture of science and arts There are rules that ensure a reasonable map: (eg map components, semiotic principles) Many additional issues to considered: Type of data to be mapped End user Acceptable generalization Experience improves map making, so you need to practice…