Summary thematic point techniques

Transcription

1 Summary thematic point techniques Dot maps Graduated symbols Bar linear (1D) proportional symbol Circle 2D proportional symbol (and other shapes) Range graded symbols classed by size Segmented symbols subdivided by subcategories Spheres 3D proportional (volumetric) symbol 1. Lines graduated lines (similar in principle to graduated bars) 1

2 Other line techniques: 2. Topological Cartograms (no fixed scale) These are based on shape and connectivity e.g. route networks; distance is relatively unimportant; The classic examples are underground maps: London 2

3 Ski map prototype example: 3. Isarithmic maps (lines of equal value) Early thematic map: Halley, Isogonic map 1701 Isogones = Lines of equal magnetic declination = difference between true north and magnetic north 3

4 Isarithms (here Isobars) lines of equal barometric pressure Some selected types of isarithms mostly climatic Isodynam Isonoet equal traffic tension average degree of intelligence 4

5 Canadian wins world Scrabble title: Isogriv CBC News Posted: Nov 08, :50 AM ET Last Updated: Nov 08, 1999 A Montreal (McGill) music professor, Joel Wapnick, has won the World Scrabble Championship Observers described Wapnick's opening move as "brilliant" because he managed to use all seven tiles to form the word "isogriv" -- a reference line on a map [a line of equal declination between magnetic and grid north] His opponent, Mark Nyman, countered with "laicized" -- which means to be free from clerical control. More than 100 players from 35 countries took part in the weekend tournament. Wapnick, won the equivalent of $22,500 Canadian. Thematic area maps: 1. Isarithms (equal values) Data are often gathered by points and interpolated to make lines/areas This is really a line technique (with ranges filled with colour tints) Average snow depth, Nov 15 use of blue to suggest snow! 5

6 Isarithm maps (here isotherms) Choice of colours selected according to the feature being mapped, e.g. blue & red for temperature, yellow for sunshine. Increased tones or chromas are being used for higher ranges; Atlas of Canada- temperature Prince George Citizen PG week review isopycnic (density) 6

7 2. Dasymetric = measure of density Dasymetric maps also depict intensities e.g. %, ratios, densities. They involve analysis beyond administrative districts; i.e. they do not assume homogeneity within districts. The lines enclosing areas are known as Isopleths 3. Qualitative (categorical) thematic area maps Software may default to using colours that are qualitatively differentiated by hue. The boundaries of such areas can be subjective and should not be interpreted as 'hard lines'. 7

8 Qualitative (categorical) data Quantitative (interval) data GIS has blurred the contrasts between qualitative (categorical) and quantitative (interval) mapping as they simply use a different attribute in the table 8

9 4. Choropleth maps = 'magnitude at place' Choropleth maps show data from collection units such as census districts or larger areas. This is used to map intensity, not absolute numbers which would be biased by larger data collection areas. Thematic mapping - choropleth 9

10 Tones or chroma are used to depict values in classes with logical ranges. Design of Choropleth Classes On Isarithmic maps, the intervals are usually even (equal-steps); But for choropleth maps: the class ranges may be changed to match the data distribution Often 'equal steps' give too many values in one class (see below) General class design goals: maximize difference between classes and minimize contrast within classes minimize or eliminate empty classes and avoid too many values in one class Example below: 5 classes 10

11 Schemes include these options: e.g. 5 classes Equal steps e.g Geometric e.g Quantiles (equal # polygons per class) Natural breaks 11

12 5. Topograms - Avoids the need to create classes, using (continuous) height 12

13 BC Mountain pine beetle infestation 6. Value-by-area cartograms a cartogram has no cartesian scale, but area is based on another geographic variable More examples: World population map Design principles: Area scale accurately represents a selected variable Contiguity is maintained Shapes should remain recognisable (if possible) 13

14 USA examples US election results: e US population cartograms and animation Cartogram software: Scape Toad 7. Cartograms Mental maps (based on perceived space) A tool of psychological research: People behave according to how they see their map People tend to: exaggerate the size and importance of their home area recall unusual features, - e.g. the Florida peninsula, 'boot' of Italy, shape of Hudson Bay, etc.. 14

15 Mental map of Canada George W. Bush's World Map 15