Thematic Mapping: Lines Flashcards
How do you map linear data?
Flow Maps
- Width of line has meaning (quantitative flow maps)
Why use a flow map?
- Dynamic
- Good for absolute data
- Shows movement of phenomena not directionality (People, goods, etc.)
- Visualize movement on a static map
How do you make a flow map?
- Most drawn by hand
- Few algorithms for automated creation
- Tobler did some work on automation in 2004
What are 3 linear data types?
- Radial
- Distributive
- Network
Radial Line Flow
Looks like a wheel with spokes
Distributive Line Flow
With Directions/arrows
- Ex. Trade Flows
Network Line Flow
Interconnectivity
Name 2 historical examples of flow maps
- Minard’s Napoleonic Military campaign
- Harness’s Dublin 1837 (1st published flow map)
Narrative Flow Maps/Diagrams.
Name some unique flow map examples.
Flow is over time not geography. Qualitative Flow
- Star Wars
- Lord of the Rings
- Dr .Who
What are three ways to represent different variables or directions in a flow map?
- Width
- Style
- Colour
ex. Going to = Red, Away from = Black
What is Nominal?
- Simple presence/abscence
- Not quantitative
- Mostly observational
- Lines differentiated by style, width, colour but there is no meaning to those choices
Mapping quantitative linear data
- May be relative (ordinal) or absolute (ratio/interval) variation in magnitude
- Variation of line width, style or colour has meaning
- Meaning is relative or absolute
Graphicacy
Ability to communicate without numbers or words but with an image
- Goal of Cartography
Line Complexity
Increasing complexity from Solid, Dashed long, Dashed short, Dot Dash long, Dot Dash short, Dot, Crosses, X+interspersed (x+x+x+x)
Rules for line complexity
- Don’t use too many (keep it simple)
- 3 is good max
- change width in line style to show message
- Use graphicacy to get message across.
Flow line details: Data Range
Smallest to largest number
Flow line details: Scaling Issues
How to deal with data range
- Width of symbol can get big fast if it is proportional to flow
Solution: Switch data with range-grading or innovate methods
Flow line details: Treatment of symbols
How to use symbols and interact with each other for visual impact
- Draw proportionally at merge points
- Scale arrowhead properly
- Interposition: small lines should appear above
Flow line details: Legend Design
- Stair step
- Range-graded
- Specified key values
Flow line details: Design Rules
- Flow lines have highest graphic importance
- Small lines appear on top of larger
- Arrows only if direction is important to map message
- Contrast between land and water are important
- Clear legends including units
- KIS
Interposition
Small lines must appear above big lines in line hierarchy
- Slight break between lines also affects the eye and makes the small line stand out more
Range-graded legend design.
- 1 point = 0-100
- 2 point = 101 - 200
etc. with symbol for each - Ensure ranges are exclusive (not 0-100, 100-200 because can’t belong to 2 groups at once)
- Exact values are better for message
Specified Key values
- 1 point = 100
- 2 point = 200
etc. - better for message
What is the problem with Corel default arrow heads for flowlines?
The default arrow head is poorly scaled to line width and doesn’t communicate magnitude for message properly
- too much where and not enough how much
Merging Lines
- Angular merge points to create flow for eye and also allows for measurement of line width at fork
- 90 degree angles are not visually appealing and don’t allow for accurate measurement
Projections
Use Equivalent when you need to preserve azimuthal direction (Only true at one point) of where or area for lines
When would you use a conformal projection?
When preserving angles
List 7 important design considerations
- Flow lines need highest visual/graphic importance
- Smaller flow lines onto of larger
- Arrows only if direction is important to map message
- Contrasts between land and water are important
- KIS, including line scaling
- Clear legends
- Simple legends that include units
Figure Ground
Figure: Objects that stand out in perception
Ground: Formless background
- from Dent
Dent’s Basic Hierarchy
1) Thematic Symbols
2) Base map: Land
3) Base map: Water features
