Map labels and legends

Adding labels to layers

Of course it is also possible to label objects in WMS. Let's add name labels to the airports:

Insert a LABELITEM object before the existing CLASS definition of airports. Then put the LABEL code inside the existing CLASS object. It should end up looking the highlighted lines in the listing below.

MAP
NAME "Thailand"
IMAGECOLOR 255 255 255
SIZE 600 800
IMAGETYPE PNG24
PROJECTION
	"init=epsg:4326" #latlon on WGS84
END #default projection
EXTENT 97.3 5.6 105.7 20.5 # lon/lat extents of Thailand
WEB
	METADATA
		"ows_enable_request" "*"
		"map" "[NETPATH]/configWMS.map"
		"ows_schemas_location" "http://schemas.opengeospatial.net"
		"ows_title" "ThailandWMS"
		"ows_onlineresource" "https://gisedu.itc.utwente.nl/cgi-bin/mapserv.exe?map=[NETPATH]/configWMS.map&"
		"ows_srs" "EPSG:4326 " #latlon      
		"wms_feature_info_mime_type" "text/plain"
		"wms_feature_info_mime_type" "text/html"
		"wms_server_version" "1.3.0"
		"wms_formatlist" "image/png,image/gif,image/jpeg"
		"wms_format" "image/png"
	END #web metadata
    VALIDATION
      "map" "*"
    END
END #web

LAYER
  NAME "forest"
  TYPE POLYGON
  STATUS ON
  CONNECTIONTYPE postgis
  CONNECTION "user=exercises password=exercises dbname=exercises host=gisedu.itc.utwente.nl port=5434 options='-c client_encoding=UTF8'"
  DATA "geom FROM thailand.forest USING UNIQUE id USING srid=4326"
  METADATA
    "ows_title" "forest"
    "ows_extent" "97.3 5.6 105.7 20.5"
  END #layer metadata
  PROJECTION
    "init=epsg:4326"
  END #layer projection
  #data attribute to use for classifying:
  CLASSITEM "for_type"
  CLASS
    NAME "Forest Reserve"
    EXPRESSION "FR" #if for_type=FR
    STYLE
      COLOR 56 168 0
    END #style
  END #class FR
  CLASS
    NAME "National Park"
    EXPRESSION "NP" #if for_type=NP
    STYLE
      COLOR 171 205 102
    END #style
  END #class NP
  CLASS
    NAME "Wildlife Sanctuary"
    EXPRESSION "WS" #if for_type=WS
    STYLE
      COLOR 245 245 122
    END #style
  END #class WS
  CLASS
    NAME "Not forest"
    EXPRESSION "NF" #if for_type=NF
    STYLE
      COLOR 200 200 200
    END #style
  END #class NF
END #layer forest
LAYER
    NAME railroad
    TYPE LINE
    STATUS ON
    CONNECTIONTYPE postgis
	CONNECTION "user=exercises password=exercises dbname=exercises host=gisedu.itc.utwente.nl port=5434 options='-c client_encoding=UTF8'"
	DATA "geom FROM thailand.railroad USING UNIQUE id USING srid=4326"
    METADATA
      "ows_title" "railroad"
  	  "ows_extent" "97.3 5.6 105.7 20.5"
    END
    PROJECTION
     "init=epsg:4326"
    END
    CLASS
      NAME "railroad"
      STYLE
        COLOR 255 0 0
        WIDTH 2
      END #style
    END #class
END #layer railroad

SYMBOL
   NAME "circle_sym"
   TYPE ellipse
   FILLED true
    POINTS
      1 1
    END
END #symbol

LAYER
    NAME airports
    TYPE POINT
    STATUS ON
    CONNECTIONTYPE postgis
	CONNECTION "user=exercises password=exercises dbname=exercises host=gisedu.itc.utwente.nl port=5434 options='-c client_encoding=UTF8'"
	DATA "geom FROM thailand.airports USING UNIQUE id USING srid=4326"
    METADATA
      "ows_title" "airports"
  		"ows_extent" "97.3 5.6 105.7 20.5"
    END
    PROJECTION
      "init=epsg:4326"
    END
    #attribute to use for labels:
    LABELITEM "name"
    CLASS
        NAME "airports"
        STYLE
          SYMBOL "airport_sym"
          SIZE 18
          COLOR 0 0 0
        END #style
        LABEL
          COLOR 0 0 0
          TYPE TRUETYPE
          FONT "arial"
          MINSIZE 5
          MAXSIZE 8
          POSITION AUTO
          PARTIALS FALSE
          BUFFER 2
        END  #label
    END #class
END #layer airports

FONTSET  "fonts/fonts.list"

SYMBOL
    NAME "airport_sym"
    TYPE TRUETYPE
    FONT "ESRI_Default_Marker"
    FILLED true
    ANTIALIAS true
    CHARACTER "o"
END #symbol

LEGEND
    KEYSIZE 16 12
    LABEL
        COLOR 0 0 0
        TYPE TRUETYPE
        FONT "arial"
        SIZE 10
    END #label
    STATUS EMBED
    POSITION LR
END #legend

END #map

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PROJECTION

"init=epsg:4326"

END

#attribute to use for labels:

LABELITEM "name"

CLASS

NAME "airports"

STYLE

SYMBOL "airport_sym"

SIZE 18

COLOR 0 0 0

END #style

LABEL

COLOR 0 0 0

TYPE TRUETYPE

FONT "arial"

MINSIZE 5

MAXSIZE 8

POSITION AUTO

PARTIALS FALSE

BUFFER 2

END #label

END #class

END #layer airports

With LABELITEM you define which attribute column in the data table has to be used for labelling. In the CLASS object you insert one (or more) LABEL objects to define how the text labels should be rendered:

COLOR to draw the text in.
TYPE of the font to use.
FONT alias as defined in the FONTSET to use for labelling.
MINSIZE tells which minimum font size to use when scaling the text
MAXSIZE tells which maximum font size to use when scaling the text
POSITION: Where to position the label text in relation to the label points. The value is a combination of vertical and horizontal positions. You have the following choices for vertical alignment: C for centre, U for upper, and L for lower. For horizontal alignment you have the following choices: C for centre, L for left, and R for right. So, to align the label text to the centre you'd use the value "CC" (centre--centre). Or if you'd like it to be on the lower left, you'd use "LL". Another way is to let MapServer decide the best position for your labels. For this you use the value AUTO.
PARTIALS: Tells MapServer whether to generate incomplete label texts or not, e.g., when the label would cross the edge of the map, or if it overlaps a label already placed. The default is not to generate fragments of a label text (PARTIALS FALSE).
BUFFER of 2 (pixels) means that no label will be drawn if another label already is within 2 pixels distance.

Adding a map legend

For a better understanding of your map it is necessary to add a legend in your map where the symbols you used are listed and named:

Create MapServer code for the legend as shown in the listing below, directly under the MAP object (in the hierarchy, so on the same level as the LAYERs and SYMBOLs). Check the results in your browser.

MAP
NAME "Thailand"
IMAGECOLOR 255 255 255
SIZE 600 800
IMAGETYPE PNG24
PROJECTION
	"init=epsg:4326" #latlon on WGS84
END #default projection
EXTENT 97.3 5.6 105.7 20.5 # lon/lat extents of Thailand
WEB
	METADATA
		"ows_enable_request" "*"
		"map" "[NETPATH]/configWMS.map"
		"ows_schemas_location" "http://schemas.opengeospatial.net"
		"ows_title" "ThailandWMS"
		"ows_onlineresource" "https://gisedu.itc.utwente.nl/cgi-bin/mapserv.exe?map=[NETPATH]/configWMS.map&"
		"ows_srs" "EPSG:4326 " #latlon      
		"wms_feature_info_mime_type" "text/plain"
		"wms_feature_info_mime_type" "text/html"
		"wms_server_version" "1.3.0"
		"wms_formatlist" "image/png,image/gif,image/jpeg"
		"wms_format" "image/png"
	END #web metadata
    VALIDATION
      "map" "*"
    END
END #web

LAYER
  NAME "forest"
  TYPE POLYGON
  STATUS ON
  CONNECTIONTYPE postgis
  CONNECTION "user=exercises password=exercises dbname=exercises host=gisedu.itc.utwente.nl port=5434 options='-c client_encoding=UTF8'"
  DATA "geom FROM thailand.forest USING UNIQUE id USING srid=4326"
  METADATA
    "ows_title" "forest"
    "ows_extent" "97.3 5.6 105.7 20.5"
  END #layer metadata
  PROJECTION
    "init=epsg:4326"
  END #layer projection
  #data attribute to use for classifying:
  CLASSITEM "for_type"
  CLASS
    NAME "Forest Reserve"
    EXPRESSION "FR" #if for_type=FR
    STYLE
      COLOR 56 168 0
    END #style
  END #class FR
  CLASS
    NAME "National Park"
    EXPRESSION "NP" #if for_type=NP
    STYLE
      COLOR 171 205 102
    END #style
  END #class NP
  CLASS
    NAME "Wildlife Sanctuary"
    EXPRESSION "WS" #if for_type=WS
    STYLE
      COLOR 245 245 122
    END #style
  END #class WS
  CLASS
    NAME "Not forest"
    EXPRESSION "NF" #if for_type=NF
    STYLE
      COLOR 200 200 200
    END #style
  END #class NF
END #layer forest
LAYER
    NAME railroad
    TYPE LINE
    STATUS ON
    CONNECTIONTYPE postgis
	CONNECTION "user=exercises password=exercises dbname=exercises host=gisedu.itc.utwente.nl port=5434 options='-c client_encoding=UTF8'"
	DATA "geom FROM thailand.railroad USING UNIQUE id USING srid=4326"
    METADATA
      "ows_title" "railroad"
  	  "ows_extent" "97.3 5.6 105.7 20.5"
    END
    PROJECTION
     "init=epsg:4326"
    END
    CLASS
      NAME "railroad"
      STYLE
        COLOR 255 0 0
        WIDTH 2
      END #style
    END #class
END #layer railroad

SYMBOL
   NAME "circle_sym"
   TYPE ellipse
   FILLED true
    POINTS
      1 1
    END
END #symbol

LAYER
    NAME airports
    TYPE POINT
    STATUS ON
    CONNECTIONTYPE postgis
	CONNECTION "user=exercises password=exercises dbname=exercises host=gisedu.itc.utwente.nl port=5434 options='-c client_encoding=UTF8'"
	DATA "geom FROM thailand.airports USING UNIQUE id USING srid=4326"
    METADATA
      "ows_title" "airports"
  		"ows_extent" "97.3 5.6 105.7 20.5"
    END
    PROJECTION
      "init=epsg:4326"
    END
    #attribute to use for labels:
    LABELITEM "name"
    CLASS
        NAME "airports"
        STYLE
          SYMBOL "airport_sym"
          SIZE 18
          COLOR 0 0 0
        END #style
        LABEL
          COLOR 0 0 0
          TYPE TRUETYPE
          FONT "arial"
          MINSIZE 5
          MAXSIZE 8
          POSITION AUTO
          PARTIALS FALSE
          BUFFER 2
        END  #label
    END #class
END #layer airports

FONTSET  "fonts/fonts.list"

SYMBOL
    NAME "airport_sym"
    TYPE TRUETYPE
    FONT "ESRI_Default_Marker"
    FILLED true
    ANTIALIAS true
    CHARACTER "o"
END #symbol

LEGEND
    KEYSIZE 16 12
    LABEL
        COLOR 0 0 0
        TYPE TRUETYPE
        FONT "arial"
        SIZE 10
    END #label
    STATUS EMBED
    POSITION LR
END #legend

END #map

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LEGEND

KEYSIZE 16 12

LABEL

COLOR 0 0 0

TYPE TRUETYPE

FONT "arial"

SIZE 10

END #label

STATUS EMBED

POSITION LR

END #legend

The LEGEND object defines the look and placement of the legend drawing:

KEYSIZE sets the size (in pixels) of the symbol key boxes
LABEL set the type, the size and the color of the font you want to use for labeling the symbol keys (see description of LABEL above).
STATUS EMBED means that the legend is embedded into the map image
POSITION sets the place within the map image. In our case on the lower-right side (LR, see POSITION described above).

The map complete with labels and a legend.

Creating an OGC Web Map Service
Using MapServer and PostGIS

Map labels and legends

Adding labels to layers

Adding a map legend

Exercise Sections

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