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1. ‹#› Muhammad Imzan Hassan Department of Geoinformatics Faculty of Geoinformation and Real Estate

2. Thematic Mapping

3. Choropleth maps These maps, where each spatial unit is filled with a uniform color or pattern , are appropriate for data that have been scaled or normalized in some way. For example, density information, expressed as "per unit area," is appropriately represented using a choropleth map. Tax rates, expressed as "per cent," are also a form of ratio data, which is most easily and correctly visualized using choropleth maps. Choropleth maps are also appropriate for indicating differences in kind of an area data, like ownership or use of land or type of forest cover. What is Choropleth Mapping?

4. What is Choropleth Mapping? Uses distinct Colour Shade Texture . . . to represent differences in value from one area to another Areal units typically administrative Can also be natural Also called enumeration area mapping

5. Two Types of Choropleth Maps 1. Conventional or Simple Areal units grouped into classes Minimum four Maximum 6 to 8 Five most common By far the more common method 2. Classless, Unclassed, or Tonal Each area assigned unique colour, shade or texture pattern Directly proportional to value No grouping into classes Difficult to detect spatial patterns

6. Examples:

7. Legend Design

8. Considerations: Symbol Selection Symbols indicate relative change in value Achieved by varying symbol: Texture Colour saturation/chroma Colour value/intensity 100 100

9. Dot Mapping What is a Dot Map? Indicates location of one or more occurrences of a geographic distribution Typically uses: abstract point symbols (best) sometimes replicative (more diff to interp.) Also called: dot density map areal frequency map

10. What is a Dot Map? Effective way of portraying variations in relative density of phenomena In theory, possible to recover original data by counting number of dots Precise location of symbols important

11. Two Types of Dot Maps One to One each dot represents one occurrence ideally, absolute location should be known Many to One each dot represents a number of occurrences e.g. 1 dot represents 1000 people common when enumeration data is utilized

12. When is it Used? or Not Used? Not preferred when: constructing large-scale maps because location of symbols representing multiple occurrences is less accurate Most appropriate when intent is to: portray variations/patterns in density/distribution compare distributions of related phenomena (i.e. show more than one thing on the same map)

13. Advantages/Disadvantages Advantages include: ease of interpretation recovery of original data ability to portray more than one distribution ease of construction (perhaps) Disadvantages include: inaccuracies in perception difficulty in extracting original data time required to construct an accurate dot map

14. Legend Design Equivalent to 1 square mile according to map scale

15. Proportional Symbol Map Shows spatial variations in value or magnitude using proportionally sized point symbols Typically circles no direction, easiest to compare but squares or replicative symbols may be used Can also use 3-D symbols to show volume May also convey density of phenomena

16. When Is It Used? When objective is to show spatial variations in value/magnitude at point locations only choice

17. Data Range NOTE : variations in attribute value must be adequately large so that there is significant differences in relative symbol size Limited variation in symbol size = boring map

18. Considerations: Symbol Selection Any point symbol that can be scaled may be used Most common is a solid circle: compact easily scaled visually stable no orientation

19. Range Graded “Proportional” Symbols

20. For replicative symbols area should also be scaled proportional Not height Proper legend design is important Double Area Double Height Determining Absolute Symbol Size

21. Considerations: Multivariate Symbols Proportional symbols, particularly circles, may be: colour coded segmented into pie type charts and inset (small circles inside of larger circles) in an attempt to portray multiple attributes

22. Symbols Design Cut-out symbols more aesthetically pleasing; less accurate Transparent circles are more accurate But can cause confusion depending on amount of base map info Symbols should be foreground objects Amount of base map info should be minimized

23. Considerations: Legend Design Three representative symbols best min, max, and medium values Nested or stacked Stacked easier to interpret Nested more compact 400 500 200 200 400 500