Welcome to Introduction to GIS Software: QGIS, Class 4

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Introduction to GIS Software: QGIS

(review)

what is metadata?

what is a qualitative thematic map?

what are expressions good for in QGIS?

adding fields to attribute tables

use a specific name

decimal number: a number with digits after the decimal point

the total digits in the number

the digits after the decimal

in-class excercise, part 1

Quantitative thematic maps

Designed Maps

Designed Maps

Designed Maps

Designed Maps

Quantitative thematic maps

often: choropleth maps

choropleth

choro: region

pleth: multitude

choropleth

a map of numbers by region

source

source

source

in-class excercise, part 2

categorizing quantitative data can be rather arbitrary

there are no natural categories

so we create categories by splitting the quantitative data into "bins"

source

source

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in-class excercise, part 3

the Modifiable Areal Unit Problem

the Modifiable Areal Unit Problem

the boundaries you create can influence the way your data looks without changing the data

the gerrymander

2012 presidential election, source

2012 presidential election, source

2012 presidential election, source

2012 presidential election, source

one way to deal with MAUP is to normalize your data

(almost) never map counts

(almost) always divide counts by some common factor

think "incidents per 100,000 people"

think "crashes per square mile"

think percentages of features in an area

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source

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normalize data with expressions in the field calculator

choropleth legends can be tricky

try to make them as readable as you can

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source

in-class excercise, part 4

you can use expressions to change details for styles

QGIS calls these "data defined overrides"

in-class excercise, part 5

overviews in print composer