You must set the symbol for the LAYER to be 'circle' and then you can set the symbol SIZE to be the width you want. A 'circle' symbol can be defined as:

SYMBOL
  NAME 'circle'
  TYPE ELLIPSE
  FILLED TRUE
  POINTS 1 1 END
END

The default output format for MapServer is 8bit pseudo-colored PNG or GIF. Inherently there will be some color degredation in converting a 24bit image (16 million colors) image into 8bit (256 colors).

But in order to ensure fast rendering MapServer uses quite a simple method to do the transformation, converting pixels to the nearest color in a 175 color colorcube. This will usually result in blotchy color in a fairly smoothly varying image.

Solutions include:

• Select 24bit output. This might be as easy as "IMAGETYPE JPEG" in your MAP section.
• Enable dithering (PROCESSING "DITHER=YES") to produce a better color appearance.
• Preprocess your image to 8bit before using it in MapServer with an external application like the GDAL rgb2pct.py script.

For more information review the Raster HOWTO document.

Although Mapscript can generate the map in any desired image format it sufficient to only consider the three most prevalent ones: JPEG, PNG, and GIF.

JPEG is an image format that uses a lossy compression algorithm to reduce an image's file size and is mostly used when loss of detail through compression is either not noticeable or negligible, as in most photos. Maps on the other hand mainly consist of fine lines and areas solidly filled in one colour, which is something JPEG is not known for displaying very well. In addition, maps, unless they include some aerial or satellite imagery, generally only use very few different colours. JPEG with its 24bit colour depth capable of displaying around 16.7 million colours is simple not suitable for this purpose. GIF and PNG however use an indexed colour palette which can be optimized for any number (up to 256) of colours which makes them the perfect solution for icons, logos, charts or maps. The following comparison (generated file sizes only; not file generation duration) will therefore only include these two file formats:

PIL does not support interlaced PNGs at this time (no timetable on when it actually will either). To be able to read PNGs in PIL, they must not be interlaced. Modify your OUTPUTFORAT with a FORMATOPTION like so:

OUTPUTFORMAT
  NAME png
  DRIVER "GD/PNG"
  MIMETYPE "image/png"
  IMAGEMODE RGB
  EXTENSION "png"
  FORMATOPTION "INTERLACE=OFF"
END

In order to render some classes of symbols properly in 24bit output, such as symbols from true type fonts, it is necessary to force rendering to occur in RGBA. This can be accomplished by including the "TRANSPARENCY ALPHA" line in the layer definition. Don't use this unnecessarily as there is a performance penalty.

This problem also affects PNG24 output or any RGB output format. 8bit (PC256) or RGBA output types are already ok.

You can use an inline feature, with the FEATURE object, to make a point on your map. Use the TEXT parameter of the FEATURE object for the actual text of the notice, and a LABEL object to style the notice.

LAYER
  NAME copyright
  STATUS ON
  TYPE annotation
  TRANSFORM ll #set the image origin to be lower left
  FEATURE
    POINTS
      60 -10 #set the offset from lower left position in pixels
    END
    TEXT "© xyz company 2006" #this is your displaying text
  END   
  CLASS
    LABEL #defines the font, colors etc. of the text
      FONT "sans"
      TYPE TRUETYPE
      SIZE 8
      BUFFER 1
      COLOR 0 0 0
      BACKGROUNDCOLOR 255 255 255
      FORCE TRUE
    END
  END 
  UNITS PIXELS #sets the units for the feature object
END

Result

For historical reasons, width has two meanings within the context of filling polygons and stroke widths for the outline. If a polygon is filled, then the width defines the width of the symbol inside the filled polygon. In this event, the outline width is disregarded, and it is always set to 1. To acheive the effect of both a fill and an outline width, you need to use two styles in your class.

STYLE # solid fill
  COLOR 255 0 0
END
STYLE # thick outline (could use a circle symbol with size too)
  OUTLINECOLOR 0 0 0
  WIDTH 3
  ANTIALIAS TRUE
END

The easiest way to produce antialiased lines is to:

• use a 24-bit output image type (IMAGEMODE RGB (or RGBA))
• set TRANSPARENCY ALPHA in the layer using antialiased lines
• set ANTIALIAS TRUE in the STYLE element of the CLASS with antialiased lines

The following mapfile snippets enable antialiased county borders:

...
IMAGETYPE png24
...
OUTPUTFORMAT
  NAME png24
  DRIVER "GD/PNG"
  MIMETYPE "image/png"
  IMAGEMODE RGB
  EXTENSION "png"
END
...
LAYER
  NAME counties
  TYPE line
  STATUS default
  DATA "bdry_counln2"
  TRANSPARENCY alpha
  SYMBOLSCALE 5000000
  CLASS
    STYLE
       WIDTH 3
       COLOR 1 1 1
       ANTIALIAS true
    END
  END
END
...

Note that the bdry_counln2 shapefile referenced in the counties layer is a line shapefile. A polygon shapefile could be substituted with roughly the same results, though owing to the nature of shapefiles each border would be rendered twice and the resulting output line would likely appear to be slightly thicker. Alternatively, one could use a polygon shapefile, set TYPE to POLYGON, and use OUTLINECOLOR in place of COLOR in the STYLE element.

Note that you can tweak the combination of STYLE->WIDTH and SYMBOLSCALE to modify line widths in your output images.

Apparently cartoline symbols can be used to achieve fancier effects.