GIST 3300 / 5300 Geographic Information Systems
Qualitative & Quantitative Thematic Data and Maps
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Introduction to Maps Introduced maps - definition of a map - basic characteristics - map scale - basic types of maps Types of maps - small scale vs large scale maps - maps classified by their function - introduced general reference, cadastral, charts, and qualitative and quantitative maps
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Today Qualitative & Quantitative Thematic Data and Maps Thematic Maps (review) Qualitative Data and Maps - text or descriptive values, ranks Quantitative Data and Maps - counts, amounts, ratios
Examples of Quantitative Thematic Mapping Methods - graduated color, graduated symbol, proportional symbol, dot density, pie chart / bar charts, isoline maps, colored or shaded rasters
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Thematic Maps (review) - Single purpose maps based on a particular theme or layer - A map on which features are symbolized based on one attribute so the map usually focuses on one particular theme or layer - Two main types - Qualitative thematic maps - Quantitative thematic maps
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Qualitative Thematic Maps - Synonyms for Qualitative: Nominal, Descriptive or Categorical - Map focuses on a particular theme or layer using qualitative or categorical values - When a layer is symbolized based on text or descriptive attributes, different features or categories are represented with a unique symbol.
Texas Counties
Different colors symbolize each county by name
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Qualitative Data
- Types of qualitative or categorical data values used to create maps can be names, types, or ranks
Different colors symbolize different state names
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Different colors symbolize different geologic types In this example, the mapped information breaks out descriptive land use types into unique values and symbolizes each with a different color. Copyright Lucia Barbato 2016 © All Rights Reserved
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Qualitative Data Classification Names or Types: Features are distinguished by a name or type and represented with a different symbol - Each value in the column (or attribute) is a unique value or different category - Name (unique values) - ex. map of states, counties or water bodies (each has a name) - Type (different categories) - ex. map of different stores, soils, land use zones (each are diff types)
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Qualitative Data Classification (also called Nominal, Descriptive or Categorical) - ranks: a qualitative value used when you are interested in relative measures - features are ranked from low to high e.g. on a scale of 1 – 5 (the actual values are not as important) 1) used when it is difficult to quantify an attribute - relative value of scenic rivers (gorgeous, scenic, not scenic) - soil types used for growing a particular crop (acceptable or not) 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)
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Qualitative Data Classification - ranks or rankings represent relative values - ex. low, medium, high - ex. poor, fair, good, excellent - ex. weak, average, strong Ex. Different line widths symbolize hurricane path by relative strength or rank: Weak (H2) – thin line Average (H3) – medium line strong (H4) – thick line
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Symbolizing Qualitative Thematic Maps - symbolizing features based on text or descriptive values is called qualitative or categorical classification Layer Properties Dialog Box
Symbology tab
Categories (for categorical / nominal / descriptive data)
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Quantitative Thematic Maps In general - Maps based on the classification of quantitative (numeric) values - Features are grouped into different classes based on a numeric attribute (using quantitative classification) Ex. Population Percent Change –
Ex. Population density – uses numeric
uses numeric information to
information divided by area (normalized) to
symbolize states.
symbolize states.
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Types of Quantitative Data - Knowing what type of quantitative data you have will help you determine how to map the values. - The types of quantitative data can be counts, amounts or ratios - counts: to see actual measured values - eg. the total number of things associated with each feature - counties mapped by their 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)
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Types of Quantitative Data - ratios: map is created by dividing two data values (normalization) Ex. Start with Top 10 States by Total Population
Population Normalized (or divided) by area Population Density By State
Ex. Micro brew map – theme or purpose is to communicate the percent adult population who drink micro brewed beer. The map groups percentages into three classes and symbolizes each group.
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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
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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
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Types of Quantitative Thematic Maps - graduated color map (choropleth map) - Choropleth maps color or shade polygons based upon the number of classes
- five pop classes - five colors
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Types of Quantitative Thematic Maps
- graduated symbol map - symbol size based upon the number of classes
- five classes - five symbol sizes
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Types of Quantitative Thematic Maps
- proportional symbol map - symbols sized proportionally to feature attribute values - no defined classes - symbol size varies directly with the value
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Types of Quantitative Thematic Maps - dot density map - each dot represents a value in the polygon layer (ex population) - number of dots in an area represents a count - this is a way to map density of features visually
- dots are placed randomly within a polygon - not actual feature locations
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Types of Quantitative Thematic Maps – Graduated Color
Layer Properties Dialog Box
Symbology tab
Quantities - Grad color - Prop color - Dot density
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Types of Quantitative Thematic Maps
- pie chart / bar chart / stacked chart maps - useful for mapping more than one variable
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Types of Quantitative Thematic Maps – Pie or Bar Charts Layer Properties Dialog Box Symbology tab
Charts
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Types of Quantitative Thematic Maps - isoline maps - used to map surfaces – vector data model – derived from a raster
Ex. isoline map - lines represent elevation contours - contour lines are overlain on a polygon layer with different color fills between the lines - polygon layer is draped over a 3D hillshade layer
- elevation contours Geographic Information Systems
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Types of Quantitative Thematic Maps
- colored or shaded rasters - used to map surfaces – using the raster data model
- Ex. color ramp applied to grid cell elevation values
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Thematic map (re-visited) - single purpose maps - shows geographic distribution of a particular theme (e.g. climate classification maps, precipitation map) Australian climate classification
Uses descriptions of climate for each color or class of features
Texas precipitation map
Uses measurements of how much precipitation is received in different parts of Texas
Qualitative or Quantitative? Geographic Information Systems
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Other types of Maps - Can have multivariate maps usually when the features are related. Sometime it is useful in seeing if there are geographical relationships between two themes – in this case pine tree diameter and their location in different vegetation zones.
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Ex. The focus of this map might be pine trees, but it is displaying two themes (pine trees and vegetation)
- Veg info is text-based, while pine tree information is numeric
Qualitative or Quantitative?
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Other types of Maps - Also temporal maps which can show change between time periods.
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Types of Quantitative Thematic Maps Summary Reference map vs Thematic map - Ref map – multi-purpose shows location of many geographic features (atlas, topographic map) - Thematic map – single purpose map shows geographic distribution of a particular theme (population, geology, land cover) Qualitative vs Quantitative - If the map theme is measured in a nominal scale it is a qualitative thematic map. Map theme is measured using names, types or ranks. Remember nominal level of information tells you simply which category (class) a feature belongs to. - If the map theme is measured in an ordinal, interval or ratio scale it is quantitative thematic map Other Maps - Multivariate – more than one theme - Temporal – introduces time, movement or change in a map Geographic Information Systems
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Lab This Week
• For your lab this you will use qualitative and quantitative mapping methods to develop several different types of maps.
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GEOGRAPHIC INFORMATION SYSTEMS Lecture 04: Quantitative Thematic Maps Qualitative Thematic Maps - qualitative thematic maps are developed based upon the classification of descriptive (categorical, nominal) data Types of Qualitative Data - quantitative data can be a names, types or ranks 1) names: (unique values) different colors used to symbolize unique names (ex. map of states, counties or water bodies) 2) types: (different categories) features are grouped by type and mapped (ex. map of different stores or land use zones) 3) ranks: features are ranked from low to high (for example, from 1 – 5 but represents relative values and not strictly numeric intervals. Values also can be descriptive) - 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)
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 or ratios 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
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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: 1) GIS Analysis: Used US Counties and US Interstates to show how GIS can be used to select features using an Attribute Query: Select By Attribute tool > ROUTE_NUM = I10 (for Interstate 10). Then we used the Select By Location tool to select features in another layer (Counties) that intersected Interstate 10. Select By Location > Selected features from Counties that intersected the Interstates. Then we obtained the population of the selected counties that were intersected by the Interstate. 2) Demonstration: of Kimble County, Texas used to illustrate the vector data model to represent how points, lines, polygons can be visualized in a GIS. Also how the raster data model is used to represent surfaces in a GIS.
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