5 Symbolizing point and linear features

What is this map type?

What do the points represent?

Graduated circle maps

uses points that have a location, but they represent a unit (typically a political unit)

What is this map type?

What do the lines represent?

Quantitative flow map

uses lines that are scaled to represent things being moved between locations

Flow map: Definition

A map used to display the movement of some phenomenon between geographic locations, generally the thickness is varied

What are 3 types of flow maps?

• origin-destination flow maps

• continuous flow maps

• trajectory-based flow maps

What are origin-destination flow maps?

Example?

portray flows between geographic locations when the actual route of flow is unimportant

Migration

What are continuous flow maps?

Example?

depict the movement of a continuous phenomenon

Wind or ocean currents

What are trajectory-based flow maps?

Example?

depict flows when the actual flow is important

Routes of members of a wolf pack over the course of several maps

What visual variables (vv) can be used for linear features?

How do you map qualitative data as lines?

What vv can be varied?

Examples?

Qualitative means feature qualites or categories

→ Vary visual variables:

• colour hue (categories)

• orientation

• texture

• shape

e.g.: traffic, borders, street types

How do you map quantitative data as lines?

What vv can be varied?

Examples?

Quantitative means numbers, varying magnitudes

→ Vary visual variables:

• color value

• color hue / saturation (categories)

• size

e.g. migration, cotton

What is the difference between qualitative or quantitative flow maps?

What vv can be varied for each?

Qualitative: What is flowing along a linear feature? e.g. wind, traffic

• orientation

• texture

• shape

Quantitative: How much is flowing along a linear feature? e.g. migration, cotton

• size

What are flow map types that are not origin-destination maps?

What are issues when designing flow maps?

• visual clutter

→ better contrast, e.g. choose a different basemap and color arrows so that the flow sits on top of the map

→ inset map

• map projection

→ global or local

• line or arrow

→ arrow if direction matters

• comprehensive legend

→ units, titles, year, explanation

What visual variables (vv) can be used for point features?

How do you map qualitative data as points?

What vv can be varied?

Examples?

Qualitative means feature qualites or categories

→ Vary visual variables:

• colour hue

• shape (geometric, mimetic)

• orientation

• texture

e.g. energy sources

How do you map quantitative data as points?

What vv can be varied?

Examples?

Quantitative means numbers, varying magnitudes

→ Vary visual variables:

• size

• colour hue / saturation

e.g. number of appartments, observed snow heights

Proportional symbol maps

• definition from glossary in book

• lab example

a map in which point symbols are scaled in proportion to the magnitude of data occurring at point locations, such as circles of varying sizes representing city populations.

Graduated symbol maps

• definition from glossary in book

• example

a term used to describe a classed proportional symbol map.

What are issues when designing graduated symbol maps?

• figure-ground contrast (cut circles)

• choice of min. / max. symbol size choice

• overlapping symbols (add ouline and transparency)

• legend types (circles horizontally, vertically, stacked inside of each other)

Dot density maps

• definition

arrangement of number points with the same magnitude

small variation of size, colour, etc

a dot can represent 1 person or 3000 people

Dot density maps

• Advantages

• Disadvantages

• Advantages

  • understandable

  • combine with other data

  • original data can be recovered

• Disadvantages

  • dots are assigned randomly

  • original values can hardly be recovered

What are issues when designing dot density maps?

• selection of number of dots

• selection of dot values

• dot size

• map scale (not too detailed, not too general)

→ dots should touch

Point symbol types

• mimetic, pictorial (graphic reduction)

• associative (typical characteristics)

• geomatric (abstraction, no relationship to represented feature)

Scaling:

Which visual dimension can be changed?

• length

• areas

• volumes

Scaling:

How are data values translated into those sizes?

• Proportional/Not classed scaling

• Range graded scaling

• Psychophysical scaling

Summary: How do you create a good map (techniques learned so far)?

choose a mapping technique according to data properties and visual/perceptual properties

Techniques:

• choropleth

• dot density

• proportional symbols

• graduated symbols

• flow map