3 Map abstraction and symbolization

VL: Week 3, Buch: Kap 4

Cartographic abstraction process

• Why is a map a model?

Map is a model that simplifies the complex reality of locations and attributes

Cartographic abstraction process

• What is the function of a map?

Mapping is at least 2D and has to be reduced in a scale-dependent way for a pragmatic use

Cartographic abstraction process

• What is the definition of map abstraction?

Process of transforming real-world phenomena or features into map elements

Cartographic abstraction process

• What are features?

anything found on the earth’s surface can be represented on a map

Features can represent different types of geographic entities:

• points

• lines

• polygons

• networks

• surfaces

→ each feature has associated attributes that provide more information (e.g. name, size, classification etc)

Cartographic abstraction process

• What do you have to know before symbolizing features?

Data model should include

• feature type (point / linear / areal)

• characteristics (discrete / discontinuous / continuous)

• measurement levels (nominal / ordinal / interval / ratio)

To make the map model by using

• map symbol (point / line / polygon)

• visual variable (size / colour value / colour hue / texture / orientation / shape)

Cartographic abstraction process

• How would you categorize different features?

• Physical (in physical geography)

• Abstract or conceptual features (in human geography)

• Process based features

Cartographic abstraction process

Physical features

• What is their inherent nature (multiple)?

• Name examples

• tangible: mountains, rivers, trees

• intangible: air masses

• Transient: earthquake

→ physical geography

Cartographic abstraction process

Abstract or conceptual features

• What is their inherent nature?

• Name examples

visible on maps:

• population density

• GDP

• district

Cartographic abstraction process

Process based features

• What is their inherent nature?

• Name examples

show change

• mud-flow

Cartographic abstraction process

• Name examples for features that can be mapped as points / lines and areas

Cartographic abstraction process

• What are discrete features?

• What are continuous features?

Refer to GEO 113 and name examples

Discrete:

• empty space with discrete features/objects

• buildings

• people

• streets

Continuous:

• Fields on which values can be measured anywhere

• earth surface

• water bodies

• ecozones

Cartographic abstraction process

In which spatial dimensions are features represented/stored in GIS?

(Spatial Dimension, represented on map, examples)

• 0D as point: e.g. building

• 1D as line: e.g. river

• 2D as area: e.g. forest

• 3D as volume: e.g. glaciers

• 4D as a volume or feature that changes over time: e.g. ocean current

Cartographic abstraction process

What are the 4 levels of measurement?

What can you do with them mathematically (in brackets)?

Properties of variables

Qualitative / Categorical

• nominal (no calculations)

• ordinal (ranking, no calculations)

Quantitative

• interval (ranking, gap between numbers relevant)

• ratio (same as interval + Ratios and percentiles reasonable)

Cartographic abstraction process

Give examples for each of the 4 levels of measurement

Qualitative / Categorical

• nominal: labels, gender, region name

• ordinal: country rank, level of difficulty

Quantitative

• interval: temperature

• ratio: number of citizens, weight, change in rent

Visual variables:

• Definition

Mapping of variations in data are shown by variations in symbols

we create a variation in the visual domain

artistic representation and scientific method

Visual variables:

Name all

• orientation

• shape

• size

• colour value

• colour hue

• texture

• colour scheme

Visual variables

• What can be symbolized with visual variables?

• name 1 example for each

• feature characteristics (e.g. continuous)

• feature spatial dimension (e.g. 1-4D)

• level of measurement (e.g. nominal)

Visual variables

• What levels of measurement can be shown with which visual variable and which spatial dimension?

• Quantitative (interval+ratio) can be shown by

  • two dimensions/size/value

  • point/line/area

• Qualitative (ordinal) can be shown by

  • texture/colour/orientation/shape

  • point/line/area

Visual variable?

1. Which vv is represented?

size shows quantitative data

Visual variable?

2. Which vv is represented?

value (lightness of the same colour)

Visual variable?

3. Which vv is represented?

colour shows qualitative difference (soil types)

Visual variable?

4. Which vv is represented? What categories exist?

colour schemes

• categorical

• unipolar

• divergent

Visual variable?

5. Which vv is represented?

texture shows mostly qualitative data

Visual variable?

6. Which vv is represented?

shape

Visual variable?

7. Which vv is represented?

orientation (here quantitative: direction of geological layers)

Visual variable:

• Applicability guideline

• name examples for qualitative/categorical and quantitative/numerical

Qualitative / Categorical

• republican/democrat

• orders, ranks

Quantitative/numerical

• magnitudes

• people / km2

• m3 of toxic waste

What is the overall cartographic principle?

Thematic relevance should correspond to perpetual salience

Choice of visual variables should match the theme

Map should be understood intuitively (e.g. no distractig colours)

Lecture summary: What are the 3 steps?

1. What data do we have?

2. What could be a fitting visual variable for this data?

3. How do we map the data?

Klicker:

• Geographical feature?

• Type?

• Spatial dimension?

• Lvl of measurement?

• Map type?

Klicker:

• Geographical feature?

• Type?

• Spatial dimension?

• Lvl of measurement?

• Map type?

Klicker:

• Geographical feature?

• Type?

• Spatial dimension?

• Lvl of measurement?

• Map type?

Klicker:

• Geographical feature?

• Type?

• Spatial dimension?

• Lvl of measurement?

• Map type?