MS RFC 45: Symbology, Labeling, and Cartography Improvements

Authors:Stephen Lime, Håvard Tveite, Thomas Bonfort
Contact:Steve.Lime at DNR.State.MN.US
Version:MapServer 5.4

(partiallly derived in part from a document prepared by Håvard and discussions with other developers working on cartographic output)

Scale Dependent Rendering

  • All symbols can be scaled. When SYMBOLSCALEDENOM is given for a layer, the layer and all of its symbols (height, width, line widths, line patterns, line dashes, ...) are scaled.
  • CLASS->STYLE->SIZE gives the vertical dimension of the symbol’s bounding box at the symbol scale (given by SYMBOLSCALEDENOM). For all other scales, the symbol is scaled proportionally to the mapscale.
  • Symbol scaling can be limited by using CLASS->STYLE->MINSIZE and CLASS->STYLE->MAXSIZE. By using these MINSIZE/MAXSIZE, one can ensure that a symbol will never be rendered smaller/larger than the given sizes.

Precise Symbol Placement

Harmonize the placement of symbols relative to the feature (point or line) being drawn.

Fractional values for sizes

All symbols sizes and symbol geometries should be specified and represented as double - AGG supports fractional line widths so users should be able to set them explicitly. GD could either round or truncate/cast the double to an int.

  • STYLE->SIZE/MINSIZE/MAXSIZE - styleObj.size/minsize/maxsize
  • STYLE->WIDTH/MINWIDTH/MAXWITH - styleObj.width/minwidth/maxwidth
  • STYLE->GAP - (replaces symbol->gap)
  • STYLE->PATTERN (new feature) - styleObj.pattern
  • STYLE-> CENTER/ORIGIN (new feature) - styleObj.centerx/centery and originx/originy
  • STYLE->OFFSET - styleObj.offsetx and styleObj.offsety
  • LABEL->SIZE/MINSIZE/MAXSIZE - labelObj.size/minsize/maxsize
  • LABEL->OFFSET - labelObj.offsetx and labelObj.offsety


Defines the centre of the symbol using decimal pixels (x axis increasing to the right, y axis increasing downwards).

  • Is used for placing a point symbol on the map or on a “decorated” line

  • Defines the center of rotation if an ANGLE is specified for point symbols.

  • Default value is the centre of the symbol’s bounding box.

  • Applies to TYPE ellipse, vector, pixmap, truetype.


    Implemented as ANCHORPOINT.


  • LABEL-> ANGLE [double|auto|follow|attribute] [DEFAULT|CLOCKWISE|COMPASS]

To specify rotation, you need a point of rotation, a reference direction, a direction of rotation and a unit of rotation.

Currently, angles for labels have a reference direction to the right (east), and a counter-clockwise direction of rotation specified in degrees (0..360).

When specifying direction/rotation for symbols, compass direction is often used (reference direction north and clockwise rotation). A mechanism to specify mode of rotation/direction is needed.

The default would be reference direction east and counter-clockwise rotation. If possible, something like:

Modes of operation

  • DEFAULT reference direction to the right (east), counter-clockwise direction of rotation.
  • CLOCKWISE reference direction to the right (east), clockwise direction of rotation.
  • COMPASS reference direction to the north, clockwise direction of rotation (compass directions).


  • For symbols of Type HATCH, this is the angle of the hatched lines.
  • For points, this specifies the rotation of a symbol around its defined CENTER.
  • For point symbols on lines, this specifies the rotation of the symbol relative to the direction of the line (0 - the symbol’s x-axis is oriented along the line), or a fixed compass direction for the symbols orientation (COMPASS).
  • For polygon fills this specifies the rotation of the pattern given by its defining symbol. For its use with hatched lines, see Example#8 in the SYMBOL examples.

Stable rendering for tile generation

how and with what keywords?

polygon fill symbols

give hatches and vector fills a stable geographical coordinate origin (0,0) to better support tiling and continuous rendering of neighbouring polygons



Keywords moved from SYMBOL to STYLE

FIXME GAP [double]+ END

Gap between point symbols when rendered on a linear geometry (used eg. for shields)

  • Given in decimal pixels (at the symbol scale). Defines distances (centre to centre) between point symbols for line decoration at the layers symbol scale

  • Default is 0.0. The first double gives the distance from the start of the line to the first point symbol, the rest of the doubles constitute a pattern of distances between the point symbols for the rest of the line.

  • GAP distances are scaled. Applies to TYPEs vector, ellipse, pixmap, truetype

  • FIXME : When drawing the symbol along a line segment, a negative GAP will add 180 degrees to the angle.

  • A GAP of 0 (the default value) will cause MapServer to use the symbol as a brush to draw the line. (AGG only)

  • The defined centre (CENTER) of the symbol is used when placing the symbol on the line. When placing the symbol on the line, the symbol is oriented in such a way that the symbol’s x-axis is directed along the line.


    INITIALGAP was introduced to address a part of this

DASHPATTERN ([double on] [double off])+ END

  • renamed from STYLE

  • the distances are scaled


    PATTERN was used instead of DASHPATTERN.

more to come?

add MINSCALEDENOM/MAXSCALEDENOM parameters to styleObj

this would allow doing things like removing outlines or the hollow portions of “tube” line work based on scale.

add LABELMETHOD to layerObj

(or perhaps just method to labelObj?)

  • this would allow users to choose label placement algorithms that meet their needs. For example, in D2 below improving label placement will come with a reduction in performance. In some situations simply using a shapes bounding box center is perfectly adequate.
  • The default would be the improved placement in D2.

add LABEL to layersObj

so that a default can be defined for all classes (sort of like templates). A class label would take precedent.

add OUTLINEWIDTH to styleObj

eg for drawing road lines with a cached outline

  • It is currently impossible to have scale dependent road networks with a fixed width outline, this addition will remedy this.
  • This would also be a shorthand to be able to specify an outline for linear networks, without having to specify two style blocks.

add TYPE to styleObj for line and polygon types

modifies how the current shape is interpreted. Applies to line and polygon layers (for now: any ideas for applying this to point layers?)

  • TYPE BBOX : use the style to render the bounding box of the current shape

  • TYPE CENTROID : render a single pointObj at the centroid of the feature

  • TYPE VERTEXES : render a pointObj at each vertex of the shape. - how to specify angle (follows line direction, fixed, ....) - need to specify a way to ignore the start and/or end points of the feature

  • TYPE START/END : render a pointObj at the start/end of the feature. would be used for example to add arrowheads to lines - default angle is direction of first/last segment


    MS RFC 48: GEOTRANSFORM Geometry operations addresses this (GEOMTRANSFORM).

Files Affected

  • maplexer.l: C4, C5
  • mapgd.c: B1, C2, C3, C4
  • mapagg.cpp: B1, C2, C3, C4
  • mapfile.c: B1, C1, C2, C3, C4, C5, C6, D1
  • mapdraw.c: C1, C5, C6, D1
  • mapprimitive.c: C5, D2

Bug IDs

Individual modifications will be tracked with their own tickets which will be listed here.