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# LEADER

Table of Contents

- LEADER

  - Description

  - Supported Layer Types

  - Mapfile Parameters

  - Mapfile Snippet

  - Example: World Countries Labels

## Description

Since version 6.2, MapServer has the ability to draw label lines to features where space is an issue for the label (often when the label text is larger than the polygon being labelled). This feature was added through MS RFC 81: Offset Labels with Leader Lines.

## Supported Layer Types

POLYGON

## Mapfile Parameters

GRIDSTEP [integer]

  Specifies the number of pixels between positions that are tested for a label line. You might start with a value of 5, and increase depending on performance (see example below).

MAXDISTANCE [integer]

  Specifies the maximum distance in pixels from the normal label location that a leader line can be drawn. You might start with a value of 30, and increase depending on the resulting placement (see example below).

STYLE

  Signals the start of a STYLE object. Use this to style the leader line.

## Mapfile Snippet

    LAYER
      NAME "my-labels"
      TYPE POLYGON
      ...
      CLASS
        ...
        LABEL
         ...
        END
        LEADER
          GRIDSTEP 5 # number of pixels between positions that are tested
          MAXDISTANCE 30 # distance in pixels that leader text can be drawn
          STYLE # normal line styles are supported
            COLOR 255 0 0
            WIDTH 1
          END
        END
      END
    END

## Example: World Countries Labels

The following example uses a polygon layer to display country labels.

Note

The data and mapfile for this example are available for download at: http://download.osgeo.org/mapserver/tickets/label-leader.zip (11MB).

### Mapfile Example #1

    MAP

    NAME "leader-test"
    STATUS ON
    SIZE 800 600
    SYMBOLSET "../etc/symbols.txt"
    EXTENT -43 10 83 83
    UNITS DD
    SHAPEPATH "../data"
    IMAGECOLOR 255 255 255
    FONTSET "../etc/fonts.txt"

    WEB
      IMAGEPATH "/ms4w/tmp/ms_tmp/"
      IMAGEURL "/ms_tmp/"
    END

    #
    # Start of layer definitions
    #

    LAYER
      NAME "continents"
      TYPE POLYGON
      STATUS ON
      DATA "world_countries-dissolve"
      LABELITEM "NA2DESC"
      CLASS
        NAME "World Countries"
        STYLE
          COLOR 200 200 200
          OUTLINECOLOR 120 120 120
        END
        LABEL
         COLOR  0 0 0
         FONT sans
         TYPE truetype
         SIZE 8
         POSITION AUTO
         PARTIALS FALSE
         OUTLINECOLOR 255 255 255
         MINFEATURESIZE 2
         MINDISTANCE 1000
         BUFFER 5
        END
        ################################
        # Leader Object
        ################################
        LEADER
          GRIDSTEP 40
          MAXDISTANCE 1000
          STYLE
            COLOR 200 100 100
            WIDTH 2
          END
        END
      END
    END

    END # Map File

### Map Image

### Mapfile Example #2

This time use a shorter maximum leader line (MAXDISTANCE) and increase the number of tests (GRIDSTEP).

    MAP

    LAYER
      ...
      CLASS
        ...
        LABEL
         ...
        END
        ################################
        # Leader Object
        ################################
        LEADER
          GRIDSTEP 10
          MAXDISTANCE 100
          STYLE
            COLOR 200 100 100
            WIDTH 2
          END
        END
      END
    END

    END # Map File

### Map Image