Example 1.1: Map with a Single Layer
MapServer can create an image and dump it to a local
directory or send it directly to the requesting web browser, as in
this example. You can view it without the need for an html page,
just enter this URL:
http://<insert hostname or IP address here>/cgi-bin/mapserv.exe?
(Remember to replace "<insert hostname or IP address here
>" with your web server's name, e.g. "localhost",
or its IP address, e.g. "127.0.0.1").
This URL can be
broken into three parts: the first part, http://<insert hostname
or IP address here>/cgi-bin/mapserv.exe?, calls the MapServer CGI
program. If you invoke it as is you will get this familiar message:
No query information to decode. QUERY_STRING is set, but empty.
The next three parts are what make up the query
string. The query string contains the CGI parameters (variables and their values), with each parameter separated by an ampersand (&). So, looking at the query string, the first parameter "map" has a value "/ms4w/apps/tutorial/htdocs/example1-1.map"--this
tells the MapServer CGI program (mapserv or mapserv.exe) what
mapfile to process/parse. The
next parameter "layer=states", tells mapserv.exe to "turn
on" the states layer--recall that we named our layer object
"states". The last parameter, "mode=map", tells
mapserv.exe what to do with the output from the mapfile. In this
case it tells mapserv.exe to dump the image directly to the web
browser (the client), without first creating a temporary image on
the server. The MapServer "mode" CGI variable takes
values other than "map". For example if you use
"mode=browse", MapServer will dump the image to a
temporary directory on the server. The browse mode will not work now
but we'll come back to it again later.
This is what the mapfile looks like (Example1-1.map):
is MapServer's basic configuration mechanism. It is made up of
"objects" and each object can have keywords or other
objects. It has a hierarchical structure such that some objects fall
under other objects... on top of this hierarchy is the MAP object,
all other objects belong to it. This example shows a very
straightforward heirarchy of objects. As you go through each
example, the complexity of these hierarchical trees will increase.
A few quick notes about mapfiles: we define each object in the
mapfile with the object name and we close it with "END"
and we precede comments with a pound (#) sign.
Let's break "example1-1.map" down by objects. Its
structure looks like this:
Let's look at the keywords (parameters) within the MAP object:
Every mapfile starts with the MAP object--the entire mapfile is the
The keyword IMAGETYPE is used to define which image format the
MapServer CGI program should use for output. In this case we are
using indexed color PNG (similar to GIF). This could be GIF, if we
compiled the GD library with GIF support, WBMP, or JPEG. We can also
specify other output options (PDF, SWF, GeoTIFF) provided that we
compiled support for them and specify them with the OUTPUTFORMAT
object. The OUTPUTFORMAT goes beyond the scope of this tutorial but
you can find out more about by reading through documentations in the
MapServer web site.
This parameter specifies the output extent of our map--the bounding
box of our initial map. The EXTENT values are given in this format:
<Lower Left X> <Lower Left Y> <Upper Right X>
<Upper Right Y>, with spaces separating each value. This needs
to be in the same units as the data or, if specifying a different
output projection, in the same units as the output projection.
In this example our data is in geographic projection so the units
are in decimal degrees. You can use the utility
which is part of the GDAL/OGR library package, to get the extent of
a particular shapefile (or other supported vector formats). Here is
the command I used to get the extent for this example:
ogrinfo -al -so states_ugl.shp
This returned the following output:
INFO: Open of `states_ugl.shp'
using driver `ESRI Shapefile' successful.
Layer name: states_ugl
Feature Count: 204
Extent: (-97.238976, 41.619778) - (-82.122902, 49.385620)
Layer SRS WKT:
AREA: Real (12.3)
PERIMETER: Real (12.3)
STATESP020: Real (11.0)
STATE: String (20.0)
STATE_FIPS: String (2.0)
CLASS: String (5.0)
You can also use ArcView or other open source GIS packages--Quantum
GIS, Thuban, etc.
Feel free to change the values of EXTENT to
get a better understanding of how it changes your map.
This is the size of the image (the map) that MapServer will
generate, in pixels. So our map is 400 pixels wide by 300 pixels
high. Again, change this to your heart's content and see how it
affects your map.
This is the path to your data layers. You can provide absolute paths
(i.e. "/ms4w/apps/tutorial/data" or
"C:/ms4w/apps/tutorial/data") or paths relative to your
mapfile's location (in this example, you'd use "../data"). This path
doesn't have to be web accessible, and probably shouldn't be unless
you want anyone to download your raw data. It has nothing directly
to do with the web so don't even think of URLs here--just make sure
that the user running the web server (usually "nobody" or
"apache" in the *nix world) can READ the data in
This is the background color of your map. The values are RGB values
so 255 Red, 255 Green, and 255B which results in a white background.
Go ahead and play with this values.
Now let's look at the LAYER object parameters:
Marks the beginning of a LAYER within the MAP object. You can
specify as many layers as you'd like although you are limited to
100, by default. To change this limit, you will have to edit the
map.h header file (in the soure tree) and recompile MapServer.
This is the layer identifier. MapServer uses this name to toggle
the layer on and off. It won't work in this example as we have the
layer STATUS set to default. We will get back to this in later
The name of the data (shapefile in this case).
Please read the MapServer Vector Data Guide
to learn more about how to access vector data in MapServer.
vector data formats other than ESRI's shapefile through the use of
OGR library (part of the GDAL software package). Please visit the
GDAL project web site at
to learn more about the various OGR supported formats.
What type of data is it? If it's a vector data, you can specify
whether it is a POLYGON, LINE (you use LINE even if your data is
technically a POLYLINE), or a POINT. You can also specify RASTER or
ANNOTATION data. Here we want to display POLYGON.
Layers are turned on or off based on their STATUS. DEFAULT is always
on. ON or OFF works when the LAYER name is passed as part of the
Let's look at the CLASS object parameters:
Marks the beginning of a CLASS object within the LAYER object. You
can specify as many classes within a layer although you are limited
to 50 by default. You'll have to recompile MapServer to change this
The descriptive identifier for this CLASS. LAYER objects can have
multiple classes, just like MAP objects can have multiple layers.
CLASS names are used by MapServer as labels for the legend so make
sure to use an appropriate descriptive name when naming classes.
We will talk about legends later in this tutorial.
And finally, let's look at the STYLE object parameters:
Marks the beginning of the STYLE object. You can define multiple
styles within a class--this is useful when you want to overlay a
style over another.
This is the fill color of the polygon. In case the TYPE is LINE,
this is the line color. The values are in RGB format.
This is the outline color of the polygons. The values are in RGB
format. MapServer doesn't draw polygon outlines by default, so if
you want to see polygon boundaries, you will want to define an
This ends the first example in this tutorial. You are encouraged to
change the values of the keywords in the mapfile. It will help you
understand what these keywords do.
Back to Section 1
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Proceed to Example 1.2