GEOGRAPHIC INFORMATION SYSTEMS
Lecture 04: Quantitative Thematic Maps
Quantitative Thematic Maps
- quantitative thematic maps are developed based upon the classification of quantitative (numerical) data
Types of Quantitative Data
- quantitative data can be a counts, amounts, ratios, or ranks
1) counts: map the total number associated with a feature
- counties mapped by total population (polygon example)
- businesses mapped by number of employees (point example)
2) amounts: map the total dollar value or magnitude associated with each feature
- gross tax revenue by county (polygons)
- per student school expenditure (points)
- earthquake magnitudes (points)
3) ratios: map the relationship between two variables (normalize)
- ratios even out the inherent difference between large and small areas
- e.g. the size of a country, state or county becomes irrelevant when mapping ratios
- most common ratios are averages, proportions, and densities
a) averages - divide quantities that use different measures
- people per household = population / number of households
b) proportions (percentages) - divide quantities that use the same measure
- percent senior citizens = population over 65 / population
c) densities - divide a quantity by the area of the feature
- population per square mile = population / square miles
4) ranks: features are ranked from low to high (for example, from 1 - 5)
- these rankings show relative values (poor, fair, good, excellent - or - low, medium, high)
- used when it is difficult to quantify an attribute
- relative value of scenic streams (low scenic value = 1, high scenic value = 5)
- soil types used for growing a particular crop (poor soils = 1, good soils = 5)
- used when a range of values is adequate for a particular purpose
- permeability of soils for a septic system (clay soils = 1, sandy soils = 5)
Types of Quantitative Thematic Maps
- there are many different ways in which quantitative data can be mapped
- graduated color map (choropleth map – colored or shaded polygons)
- graduated symbol map (symbol size varies based upon the number of classes)
- proportional symbol map (symbols sized varies proportionally to feature attribute values)
- dot density map (number of dots in an area represents a count (e.g. 1 dot = 500 dairy cows)
- pie chart / bar chart / stacked chart maps (useful for mapping more than one variable)
- isoline maps - used to map surfaces, vector lines derived from rasters (e.g. contours, isobars, isotherms)
- colored or shaded rasters - used to map surfaces (color or shades vary with grid cell values)
- demonstration illustrating how we create the different types of quantitative thematic maps (next class)
Copyright© 2015, Kevin Mulligan, Texas Tech University
GIST 3300 / 5300
Geographic Information Systems
Quantitative Thematic Maps
Types of Quantitative Data
- counts, amounts, ratios and ranks
Types of Quantitative Thematic Maps
- graduated color, graduated symbol, proportional symbol, dot density,
pie chart / bar charts, isoline maps, colored or shaded rasters
Geographic Information Systems
Quantitative Thematic Maps
- maps based on the classification of quantitative (numerical) data
In general
- Knowing what type of data you have will help you determine
what quantitative value to map
Types of Quantitative Data
- these quantitative data can be counts, amounts, ratios or ranks
Geographic Information Systems
Types of Quantitative Data
- these quantitative data can be counts, amounts, ratios or ranks
- counts: to see actual measured values
- eg. map the total number of things associated with each feature
- counties mapped by total population (polygon example)
- businesses mapped by number of employees (point example)
- amounts
- eg. map total dollar value or magnitude associated with each feature
- gross tax revenue by county (polygons)
- per student school expenditure (points)
- earthquake magnitudes (points)
Geographic Information Systems
Types of Quantitative Data
- ratios: map is created by dividing two data values (normalize)
- map the relationship between two variables
- evens out differences between large and small areas
Top 10 States by Population
Top 10 States by Population Density
(population normalized by area)
Geographic Information Systems
Types of Quantitative Data
- ratios
- map the relationship between two variables
- evens out difference between large and small areas
- most common ratios are averages, proportions, and densities
- averages
- divide quantities that use different measures
- people per household = population / number of households
- proportions (same as percentages)
- divide quantities that use the same measure
- percent under age 5 = population under 5 / population
- densities
- divide a quantity by the area of the feature
- population per square mile = population / square miles
Geographic Information Systems
Types of Quantitative Data
- ranks: use when you are interested in relative measures
- features are numerically ranked from low to high
e.g. on a scale of 1 – 5 (actual values are not as important)
- these rankings show relative values
- poor, fair, good, excellent
- low, medium, high
1) used when it is difficult to quantify an attribute
- relative value of scenic rivers
- soil types used for growing a particular crop
2) used when a range of values is adequate for a particular purpose
- permeability of soils for a septic system
- clay soils ranked low (1)
- sandy soils ranked high (5)
Geographic Information Systems
Types of Quantitative Thematic Maps
- graduated color map (choropleth map)
- colored or shaded polygons based upon the number of classes
- graduated symbol map
- symbol size based upon the number of classes
- proportional symbol map
- symbols sized proportionally to feature attribute values
- dot density map
- number of dots in an area represents a count
- pie chart / bar chart / stacked chart maps
- useful for mapping more than one variable
- isoline maps
- used to map surfaces – vector data model – derived from a raster
- colored or shaded rasters
- used to map surfaces – raster data model
Geographic Information Systems
Types of Quantitative Thematic Maps
- graduated color map (choropleth map)
- colored or shaded polygons based upon the number of classes
- five classes
- five colors
Geographic Information Systems
Types of Quantitative Thematic Maps
- graduated symbol map
- symbol size based upon the number of classes
- five classes
- five symbol sizes
Geographic Information Systems
Types of Quantitative Thematic Maps
- proportional symbol map
- symbols sized proportionally to feature attribute values
- no defined classes
- symbol size varies directly with attribute value
Geographic Information Systems
Types of Quantitative Thematic Maps
- dot density map
- number of dots in an area represents a count
- dots are placed randomly within a polygon
Geographic Information Systems
Types of Quantitative Thematic Maps
- pie chart / bar chart / stacked chart maps
- useful for mapping more than one variable
Geographic Information Systems
Types of Quantitative Thematic Maps
- isoline maps
- used to map surfaces – vector data model – derived from a raster
- elevation contours
Geographic Information Systems
Types of Quantitative Thematic Maps
- colored or shaded rasters
- used to map surfaces – raster data model
- color ramp applied to grid cell elevation values
Geographic Information Systems
Types of Quantitative Thematic Maps
Layer Properties Dialog Box
Symbology tab
Quantities
Geographic Information Systems
Types of Quantitative Thematic Maps
Layer Properties Dialog Box
Symbology tab
Charts
Geographic Information Systems