Vorlesung 5; scale & generalization

spatial (pixel size, polygon count)

temporal (recording frequency)

attribute

small: 1:500'000 oder kleiner, am wenigsten Details, grösste räumliche Ausdehnung (z.B. Landkarte)

medium: weniger räumliche Ausdehnung (z.B. Stadtkarte)

large: 1:10'000 oder grösser, am meisten Details, kleinste räumliche Ausdehnung (z.B. Campuskarte)

areal scale: area size on map vs. in reality

linear scale: linear distance on map vs. in reality

- Representative fraction (RF): numerischer Massstab, z.B. 1:500'000

- Verbal Statements: Beziehung zw. Kartendistanz & Bodendistanz, z.B. "one cm represents one km"

- Graphic Scales: graphic symbol to represent relationship of map units to ground units, z.B. bar scale

+ intuitiv

- besteht Grössenwechsel nicht (hinein-/hinauszoomen)

bestehen bei Grössenwechsel

...Kunst (subjektiv): was sieht gut aus, Ästhetik

...Wissenschaft (objektiv): Regeln, Gesetze

Klassierung und Auswahl der Objekte von Verkehrsnetz, Bebauung, Gewässer, Vegetation

grafische Generalisierung, lagegenaue & wahrheitsgetreue Darstellung der ausgewählten Objekte unter Wahrung der charakteristischen Form

1. selection

2. classification

3. simplification

(4. symbolisation)

to keep readable at different scales

consequence of scale change

consequence of purpose & audience

- bei Überfüllung

- bei Kollisionen

- bei Konflikten

-bei Komplikationen

- simplification: select critical points, eliminate maximum nr. of coordinates, retain as much of the geometry as possible

- smoothing: shifts object position to improve appearence

- aggregation: merging clusters of points in area

- amalgamation: fusing individual small areas in larger areas

- merging: fusing gropus of lines

- collapse: replacing objects of detailed form by a representative symbol

- refinement: selecting specific portion of an object to represent object

- exageration: making map features larger

- enhancement: controlled & purposeful introduction of detail

- displacement: separating objects

how many features to keep at smaller scales?

N_c = N_o * Wurzel(S_o/S_c)         (evtl. * c_p * c_f)

N_c: number of objects at created scale (= to keep)

N_o: number of original objects

S_c: scale denominator created

S_o: scale denominator original

c_p: map purpose constatn

c_f: symbol size

- graphic density (> 30% black ink)

- just noticable difference (features colliding due to scale change)

- visual perception characteristics (smallest type not below 1.2mm, smallest point not below 0.1mm)

- Map purpose:

    - map type (reference, navigational, thematic)

    - target audience (expert vs. child)

    - time available to read (on the road)

    - lighting conditions (star gaze map, underwater map)

- Data quality (availability of data? source?)

-Storage space (size of digital file)