label placement rules, techniques. labels on a map text, name of map features no fixed geographical...

Label placementRules, techniques

Labels on a map• Text, name of map features• No fixed geographical position• Labels of point features (0-dim), line features (1-

dim), areal features (2-dim)

Labels of point features

• Cities on a small-scale map• Heights of peaks• Measured values at measurement points

Labels of point features

Touristic sights, campgrounds

Labels of line features

• Rivers• Heights on contour lines• Streets

Labels of line features

Labels of areal features

• Countries, oceans, forests, lakes

Labels of areal features

Three kinds of labels

Utrecht

Nieuwegein Houten

Culemborg

Straight, horizontal name

Curved name Spacing between characters

Label placement

• Where should the text be placed? Which shape? • 20% - 50% of the manual map production time;

can be automated• Which rules do cartographers use?

- No overlap readability- Clear for which feature association- Aesthetical guidelines

Example

Eduard Imhof (1895-1986)

- Swiss Cartographer- “Positioning Names on

Maps” (1962/1975)

Rules according to Imhof

Problematic cases

Problem visibility highway 20

Problem association Thunder Bay and point

Problem readability name

Another problematic case

University Ave. is interrupted 4 times

Specific rules point labels• Label must be close to point,

preferably to right and above• Labels are placed horizontal,

no extra spacing• No overlap with other labels,

except perhaps in the spacing of the areal label

• Label may intersect line feature; then line must be interrupted

• Points at a large body of water must have their label in the water. In other cases there may be no line between a point and its label

• If it cannot be avoided, a name may be split over two lines of text

Specific rules line labels• Label must follow shape of river• Label should not bend upwards

and downwards consecutively• At long line features the label

must be repeated• No or little extra spacing

between characters, spacing between words of the label is allowed

• For vertical line features: upward reading direction left on the map and downward right on the map

• Contour lines: labels must interrupt contour line; top of label points to higher regions

Specific rules areal labels

• Horizontal labeling is good unless this conflicts with the dominant shape of the region

• Non-horizontal labels must be curved

• Monotonous curving; no inflection points

• Label should be spread over whole region

• Adjacent regions preferably have same shape of label (both horizontal, e.g.)

• Sometimes an areal label may be outside its region, but not in another labeled region

• Small areal features treated as point features

Strategies for automatic label placement

• Compute for each feature various candidate positions according to the rules

• Choose for each feature one candidate position, such that the chosen positions do not overlap

• Sometimes a feature cannot be labeled, and sometimes the label of a feature must be repeated

Candidate positions points

• Point labels

4-position model

8-position model

slider modelMore general model more labels can be placed, but more complex/ expensive to compute

Candidate positions points

• Priority of point label positions

Imhof 5 43

2 1

Ebinger4

3

2

1

Jones 23

1

Zoraster

56

4

47

258

3 1

6

Yoeli,Hirsch 3

1

4

2 5

6

10

9

8

7

Candidate positions lines

• Compute strip with character height above the river which follows the shape approximately, but doesn’t have too high curvature (e.g. with opening, closure)

• Determine suitable segments in the strip as candidates

Candidate positions regions

• Determine skeleton (medial axis) of region (polygon)

• Determine longest path on skeleton as dominant shape

• Choose middle with suitable character spacing• Vary a little for more candidates

Candidate positions regions, horizontal

• Choose spacing and determine length : height of label

• Compute largest scaled copy of the label (rectangle) that just fits inside the polygon

• Put the label in the correct font size in the middle of the scaled copy

B e l g i ë

B e l g i ë B e l g i ë

Removal part of the candidates

• Compute those candidate positions that intersect map features significantly, or would give unclear association, and remove them

Nieuwegein

NieuwegeinNieuwegein

poor poor good

Reasons for removal

Utrecht

Utrecht

Utrecht

Utrecht

UtrechtZeist

Zeist

Readability text

Visibility features

Association

Utrecht

poor

good

Choosing from the candidates

• Translate to a graph problem (graph G):- each candidate position of each feature is a node in G- two nodes have an edge in G if their candidate positions intersect- two nodes have an edge in G if their candidate positions are of the same feature

Example

UtrechtUtrecht

UtrechtUtrecht

BunnikBunnik

BunnikBunnik

Computing intersecting candidates

• Each candidate is (approximately) a simple geometric shape

• Determine all pairs of intersecting candidates using a plane sweep algorithm

• O((n+k) log n) time, with k the number of intersecting pairs

• Typically: k = O(n)

• Independent set: Set of vertices W with for all v, w W: {v,w} E.

• Maximum independent set problem: find largest independent set

• Clique: Set of vertices W with for all v, w W: {v,w} E.

Independent Set

Clique

Graph problem: maximum independent set

Graph problem: maximum independent set

• Also called maximum stable set

• NP-hard problem: solving optimally is very time consuming

• Cannot be approximated with performance guarantees

• Many heuristics

Independent Set

Heuristics for maximum independent set

• Select each candidate that is only adjacent to a clique, and remove the candidate and clique from the graph

• Repeat as long as possible (optimal selections)




Utrecht Bunnik




• Select candidate that intersects few other candidates

• Select candidate if a feature has only one(or a few) candidates left

• Eliminate candidates that intersect many candidates

Refinements

• Features and labels have different importances• Candidates can have different priority translate problem to maximum weight

independent set

• First place areal labels, then determine candidate point labels and select, then determine line labels and place them(order of decreasing freedom of placement)

Labels in GIS

• Can label positions be pre-computed and stored, for better efficiency?

No, because– Which themes are shown is not known

beforehand;– Which scale and size of the map is needed is

not known beforehand

Labels on interactive maps

• Pop-up labels, or labels only after click• During zooming in, remove labels when their

feature goes outside the frame• During zooming in, allow more and more labels;

during zooming out, remove labels of less important featuresSize of labels does not change!

Labels on interactive maps

Commercial packages

• Maplex for ESRI’s ArcInfo and ArcGIS• Label-EZ/MapText for ArcInfo, ArcGIS,

MapInfo, GeoMedia, …• EverName for MapInfo

Maplex: Label fitting & conflicts

• Label Fitting Strategies– Label Stacking– Font Reduction– Abbreviation

• Conflict Resolution– Feature Priority– Overlapping– Creating background labels– Remove duplicate

Maplex: Label position

Maplex: Label fitting

• Points


• Lines


• Area

Maplex: Conflict resolution

MapText/Label-EZ

• Configuration file

Cartographic placement rules and preferences according to map type

• Label Fitting Strategies– Reduce font size– Place names with leaders– Use key numbers if no other

possibility for overprint-free placement is possible.

MapText: Label Position

EverName: Label position

EverName: Output

Label Placement - Summary

• Cartographic rules for point features, line features, and areal features

• Strategies for automatic label placement– Compute Candidates– Select Candidates: Maximum independent

Set Problem

• Commercial packages for label placement

label placement rules, techniques. labels on a map text, name of map features no fixed geographical...

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