Sequential Color Schemes • Ideal for mapping ordered data that goes from low to high • Light colors = low values and darker colors = higher values
Diverging Color Schemes • Equal emphasis on mid-range critical values & extremes at both ends of the data range – The critical class or break in the middle of the legend is emphasized with light colors and low & high extremes are emphasized with dark colors that have contrasting hues
Color Considerations in Maps • Things to consider : – Colors for the color blind – Alert to color associations that may be offensive – Colors that can be suitable for black & white reproduction – Use appropriate color ramps – Lighter colors for lower values and Darker colors for higher values – Maintain logical color relationships (forest type) – Group colors to make quick scanning of map efficient
Color Considerations in Maps Contrast for emphasis is good, but…
Basic Map Types 1. Feature – points, lines, or areas (nominal info) most common map type (road maps) 2. Choropleth – depict quantitative information (pop per sq/mile map) Source: Paul Bolstad. 2016. GIS Fundamentals – A first text on Geographic Information Systems. 5 th ed.
Basic Map Types 1. Dot density – also depict quantitative data…dots represent a value 1. Isopleth – contour maps display lines of equal value (temp maps) Source: Paul Bolstad. 2016. GIS Fundamentals – A first text on Geographic Information Systems. 5 th ed.
Choropleth Maps • Choropleth = mapping spatial values by place, or more precisely, enumeration units (EUs) – Statistical or political units by which the data is gathered. • Appropriate when: – Data when data are DISCRETE – Data are derived , NOT total (EUs are unequal in area!) - data can be expressed as ratios or proportions
Choropleth Mapping Considerations 1. Standardization - size and shapes of the enumeration units can impact how variables are presented 2. Number of class intervals 1. Too few classes too general impression of relationships Too many too noisy, present relationship that may not exist 3. Class intervals- Different types of class intervals affect how data is represented 1. Natural breaks, Equal Interval, Quantile, etc. 4. Symbolization - color decisions are important for symbolizing relationships accurately 1. Sequential color scheme (i.e. income, population density) 2. Diverging Color scheme (i.e. Republicans, vs. Democrats)
Choropleth Mapping Considerations Enumeration unit = State Enumeration unit = County
Choropleth Mapping Considerations • Defined Interval – user defines class intervals and value ranges • Quantile – puts same number of features in each class – Best applied to linear data • Geometric interval – classes based on geometric series – Best for continuous data • Standard Deviation – apportions classes based on statistics of field – Best for highlighting outliers
Choropleth Symbolization Two schools of thought… 1. Pattern density or contrast is most important –
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- Fall '08
- Cartography, thematic map, Choropleth Symbolization