faq.txt

.. _faq:

***************************************************
 常见问题
***************************************************

Server将日志文件放在什么位置？
-------------------------------------------------------------------------------

参见 :ref:`rfc28`

学习MapServer可以参考哪些书籍？
-------------------------------------------------------------------------------

`"Mapping Hacks" <http://www.oreilly.com/catalog/mappinghks/>`__ Schuyler
Erle，Rich Gibson和Jo Walsh著，O'Reilly出版。

`"Web Mapping Illustrated" <http://oreilly.com/catalog/webmapping>`__ Tyler
Mitchell著，O'Reilly出版。本书介绍了MapServer及其他许多相关的技术，包括GDAL/OGR，MapScript，PostGIS和地图投影等。

`"MapServer: Open Source GIS Development"
<http://www.apress.com/book/bookDisplay.html?bID=443>`__ Bill Kropla著。


如何在Windoes上编译编译MapServer？
-------------------------------------------------------------------------------

参见 :ref:`win32` 同时，您也可以 :ref:`OSGeo4W <windows>` 的库作为入门使用，这样就不用自行编译所有的库

MapServer的版本号有什么特别的意思？
-------------------------------------------------------------------------------

MapServer的版本路线图与Linux的十分相似。例如，MapServer 4.2.5的版本号代表着：

- 4：主版本号。MapServer每两到三年会发布一个新的主版本。
- 2：次版本号。次版本号与每次的添加功能有关。
- 5：修正版本号。修正版意味着不添加新功能，只进行BUG修复。

从开发者的角度看，MapServer的版本路线图跟Linux的开发版本号也是很类似:偶数的次版本号（0..2..4..6）代表着稳定版本，奇数（1..3..5..7..9）代表着开发版本。

MapServer是否线程安全的？
-------------------------------------------------------------------------------

** 问 ** ：MapServer是否线程安全的？

** 答 ** ：总的来说，不是（请同阅下一个问题）。 MapServer 的许多组建使用静态变量或全局变量，这些变量的值都有被其他线程修改的可能。重复加载这些组建不可避免，并且可能会导致一些错误。

** 问 ** ：能够在多线程程序中安全地使用MapServer或者其组建吗？

** 答 ** ：有一些可以很谨慎地加以使用。对于 Python 程序员来说，他们必须谨慎地选择使用 MapServer 组件，同时还得要在恰当的地方加上锁。 Python 的全局解释器锁加大 MapServer 的线程问题；由于 mapscript 代码都没有 GIL，所有的 mapscript 函数赫方法都是原子的。 mapscript 和 Java、.Net、mod_perl、或 mod_php 并没有这一层额外的安全机制。

** 问 ** ：那些组件需要避免使用？

** 答 ** ：以下是一些不安全的组件、未受保护的组件和不安全但被锁定的组件列表：

不安全的组件：

- OGR layers: use unsafe CPL services 
- Cartoline rendering: static data
- Imagemap output: static data
- SWF output: static data and use of unsafe msGetBasename()
- SVG output: static data
- WMS/WFS server: static data used for state of dispatcher
- Forcing a temporary file base (an obscure feature): static data
- MyGIS: some static data

不安全但被锁定的组件：

- Map config file loading: global parser
- Setting class and and layer filter expressions (global parser)
- Class expression evaluation (global parser)
- Setting map and layer projections (PROJ)
- Raster layer rendering and querying (GDAL)
- Database Connections (mappool.c)
- PostGIS support
- Oracle Spatial (use a single environment handle for connection)
- SDE support (global layer cache)
- Error handling (static repository of the error objects)
- WMS/WFS client connections: potential race condition in Curl initialization
- Plugin layers (static repository of the loaded dll-s)

Rather coarse locks are in place for the above. Only a single thread can use
the global parser at a time, and only one thread can access GDAL raster data
at a time. Performance is exchanged for safety.

What does STATUS mean in a LAYER?
-------------------------------------------------------------------------------

STATUS ON and STATUS OFF set the default status of the layer. If a map is
requested, those layers will be ON/OFF unless otherwise specified via the
layers parameter. This is particularly the case when using MapScript and
MapServer's built-in template mechanism, but is also useful as a hint when
writing your own apps and setting up the initial map view.

STATUS DEFAULT means that the layer is always on, even if not specified in the
layers parameter. A layer's status can be changed from DEFAULT to OFF in
MapScript, but other than that, it's always on.

:ref:`cgi` turns everything off that is not "STATUS DEFAULT" off so all layers
start from the same state (e.g. off) and must be explicitly requested to be
drawn or query. That common state made (at least in my mind) implementations
easier. I mean, if a layer "lakes" started ON the doing layer=lakes would turn
it OFF. So I wanted to remove the ambiguity of a starting state.

How can I make my maps run faster?
-------------------------------------------------------------------------------

There are a lot of different approaches to improving the performance of your
maps, aside from the obvious and expensive step of buying faster hardware.
Here are links to some individual howtos for various optimizations.

* :ref:`Tuning your mapfile for performance <mapfile_tuning>`
* :ref:`Optimizing the performance of vector data sources <vector_optimization>`
* :ref:`Optimizing the performance of raster data sources <raster_optimization>`
* :ref:`Tileindexes for mosaicing and performance <tileindex>`

Some general tips for all cases:

* First and foremost is hardware. An extra GB of RAM will give your map
  performance increases beyond anything you're likely to achieve by tweaking
  your data. With the price of RAM these days, it's cheap and easy to speed up
  every map with one inexpensive upgrade.

* Use the scientific method. Change one thing at a time, and see what effect
  it had. Try disabling all layers and enabling them one at a time until you
  discover which layer is being problematic.

* Use :ref:`shp2img` program to time your results. This runs from
  the command line and draws an image of your entire map. Since it's run from
  the command line, it is immune to net lag and will give more consistent
  measurements that your web browser.

What does Polyline mean in MapServer?
-------------------------------------------------------------------------------

There's confusion over what POLYLINE means in MapServer and via ESRI. In
MapServer POLYLINE simply means a linear representation of POLYGON data. With
ESRI polyline means multi-line. Old versions of the Shapefile techical
description don't even refer to polyline shapefiles, just line. So, ESRI
polyline shapefiles are just linework and can only be drawn and labeled as
LINE layers. Those shapefiles don't have feature closure enforced as polygon
shapefiles do which is why the distinction is so important. I suppose there is
a better choice than POLYLINE but I don't know what it would be.

.. note::
    The only difference between POLYLINE and LINE layers is how they are
    labeled.

What is MapScript?
-------------------------------------------------------------------------------

MapScript is the scripting interface to MapServer, usually generated by 
:term:`SWIG` (except in the case of :ref:`php`).  MapScript allows you to 
program with MapServer's objects directly instead of interacting with 
MapServer through its :ref:`cgi` and :ref:`mapfile`.


Does MapServer support reverse geocoding?
-------------------------------------------------------------------------------

No.

Reverse geocoding is an activity where you take a list of street features that
you already have and generate postal addresses from them. This kind of spatial
functionality is provided by proprietary packages such as the ESRI suite of
tools, as well as services such as those provided by GDT. MapServer is for
*map rendering*, and it does not provide for advanced spatial operations such
as this.

Does MapServer support geocoding?
-------------------------------------------------------------------------------

No.

Geocoding is an activity where you take a list of addresses and generate
lat/lon points for them. This kind of spatial functionality is provided by
proprietary packages such as the ESRI suite of tools, as well as services such
as those provided by GDT. MapServer is for *map rendering*, and it does not
provide for advanced spatial operations such as this.

If you are using MapScript, there is a free geocder available through XMLRPC
and SOAP at http://geocoder.us . You could hook you application up to use this
service to provide lat/lon pairs for addresses, and then use MapServer to
display those points.

How do I set line width in my maps?
-------------------------------------------------------------------------------

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

.. code-block:: mapfile

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

Why do my JPEG input images look crappy via MapServer?
-------------------------------------------------------------------------------

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 :ref:`raster`.

Which image format should I use?
-------------------------------------------------------------------------------

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:

.. table:: GIF vs. PNG vs. PNG24 Generated Map File Sizes                   

    +------------------------------------------+-------+-------+-------+
    |                                          | GIF   | PNG   | PNG24 |
    +==========================================+=======+=======+=======+
    |Vector Data only                          | 59kb  | 26kb  | 69kb  |
    +------------------------------------------+-------+-------+-------+
    |Vector Data & Satellite Image coloured    | 156kb | 182kb | 573kb |
    +------------------------------------------+-------+-------+-------+
    |Vector Data & Satellite Image monochrome  | 142kb | 134kb | 492kb |
    +------------------------------------------+-------+-------+-------+

(results based on an average 630x396 map with various colours, symbols,
labels/annotations etc.)

Although GIF shows a quantitative as well as qualitative advantage over PNG
when generating maps that contain full coloured remote sensing imagery, PNG is
the clear quantitative winner in terms of generated file sizes for maps with
or without additional monochrome imagery and should therefore been the
preferred image format. If the mapping application however can also display
fullcolour aerial or satellite imagery, the output file format can be changed
dynamically to either GIF or even PNG24 to achieve the highest possible image
quality.

Why doesn't PIL (Python Imaging Library) open my PNGs?
-------------------------------------------------------------------------------

`PIL <http://www.pythonware.com/products/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 OUTPUTFORMAT with
a FORMATOPTION like so:

.. code-block:: mapfile

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

Why do my symbols look poor in JPEG output?
-------------------------------------------------------------------------------

When I render my symbols to an 8bit output (PNG, GIF) they look fine, but in
24bit jpeg output they look very blocky and gross.

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.

How do I add a copyright notice on the corner of my map?
-------------------------------------------------------------------------------

You can use an inline feature, with the :ref:`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 :ref:`LABEL` object to style the notice.

Example Layer
...............................................................................

.. code-block:: mapfile

    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
...............................................................................

.. image:: ./images/copyright-image.png


How do I have a polygon that has both a fill and an outline with a width?
-------------------------------------------------------------------------------

How do I have a polygon that has both a fill and an outline with a width?
Whenever I put both a color (fill) and an outlinecolor with a width on a
polygon within a single STYLE, the outline width isn't respected.

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.

.. code-block:: mapfile

    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

How can I create simple antialiased line features?
-------------------------------------------------------------------------------

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:

.. code-block:: mapfile

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

.. seealso::
    :ref:`Cartoline <sym_construction>` symbols can be used to achieve fancier
    effects.
 
Which OGC Specifications does MapServer support?
-------------------------------------------------------------------------------

See: :ref:`OGCSUPPORT`

Why does my requested WMS layer not align correctly?
-------------------------------------------------------------------------------

Requesting a layer from some ArcIMS WMS connectors results in a map with
misalgned data (the aspect ratio of the pixels looks wrong).

Some ArcIMS sites are not set up to stretch the returned image to fit the
requested envelope by default. This results in a map with data layers that
overlay well in the center of the map, but not towards the edges. This can be
solved by adding "*reaspect=false*" to the request (by tacking it on to the
connection string).

For example, if your mapfile is in a projection other than EPSG:4326, the
following layer will not render correctly:

.. code-block:: mapfile

    LAYER
        NAME "hillshade"
        TYPE RASTER
        STATUS OFF
        TRANSPARENCY 70
        CONNECTIONTYPE WMS
        CONNECTION "http://gisdata.usgs.net:80/servlet19/com.esri.wms.Esrimap/USGS_WMS_NED?"
        PROJECTION
        	"init=epsg:4326"
        END
        METADATA
        	"wms_srs" "EPSG:4326"
        	"wms_title" "US_NED_Shaded_Relief"
        	"wms_name" "US_NED_Shaded_Relief"
        	"wms_server_version" "1.1.1"
        	"wms_format" "image/png"
        END
    END

Adding "reaspect=false" to the connection string solves the problem:

.. code-block:: mapfile

    LAYER
        NAME "hillshade"
        TYPE RASTER
        STATUS OFF
        TRANSPARENCY 70
        CONNECTIONTYPE WMS
        CONNECTION "http://gisdata.usgs.net:80/servlet19/com.esri.wms.Esrimap/USGS_WMS_NED?reaspect=false"
        PROJECTION
        	"init=epsg:4326"
        END
        METADATA
        	"wms_srs" "EPSG:4326"
        	"wms_title" "US_NED_Shaded_Relief"
        	"wms_name" "US_NED_Shaded_Relief"
        	"wms_server_version" "1.1.1"
        	"wms_format" "image/png"
        END
    END

When I do a GetCapabilities, why does my browser want to download mapserv.exe/mapserv?
---------------------------------------------------------------------------------------

A beginner question here... I'm new to MS and to Apache. I've got MS4W up and
running with the Itasca demo. Now I want to enable it as a WMS server. mapserv
-v at the command line tells me it supports WMS_SERVER. When I point my
browser to it, my browser just wants to download mapserv.exe!

What am I missing?

Here is the URL I'm using to issue a GetCapabilities WMS request:
http://localhost/cgi-bin/mapserv.exe?map=../htdocs/itasca/demo.map&SERVICE=WMS&VERSION=1.1.1&REQUEST=GetCapabilities

The OGC:WMS 1.1.0 and 1.1.1 specifications (which are both supported by
MapServer) state that, for GetCapabilities responses, the OGC:WMS server
returns a specific MIME type (i.e. application/vnd.ogc.xml (see subclause
6.5.3 of `OGC:WMS 1.1.1
<https://portal.ogc.org/files/?artifact_id=1081&version=1&format=pdf>`__.

A MIME type is passed from the web server to the client (in your case, a web
browser), from which a client can decide how to process it.

Example 1: if using a web browser, if a web server returns an HTTP Header of
"Content-type:image/png", then the web browser will know that this is a PNG
image and display it accordingly.

Example 2: if using a web browser, if a web server returns an HTTP Header of
"Content-type:text/html", then the web browser will know that this is an HTML
page and display it accordingly (i.e. tables, divs, etc.)

Basically, what is happening is that the OGC:WMS is returning, in the headers
of the HTTP response, a MIME type which your web browser does not understand,
which usually prompts a dialog box on whether to open or download the content
(i.e. Content-type:application/vnd.ogc.wms_xml).

You could configure your web browser to handle the application/vnd.ogc.wms_xml
MIME type a certain way (i.e. open in Notepad, etc.).

Why do my WMS GetMap requests return exception using MapServer 5.0?
-------------------------------------------------------------------------------

Before upgrading to MapServer 5.0, I was able to do quick GetMap tests in the
form of:
http://wms.example.com/wms?service=WMS&version=1.1.1&request=GetMap&layers=foo

Now when I try the same test, MapServer WMS returns an XML document saying
something about missing required parameters. What's going on here?

This was a major change for WMS Server support in MapServer 5.0. MapServer WMS
Server GetMap requests now require the following additional parameters:

* srs
* bbox
* width
* height
* format
* styles

.. note:: 
    These parameters were always required in all versions of the WMS
    specification, but MapServer previously had not required them in a client
    request (even though most OGC WMS clients would issue them anyway to be
    consistent with the WMS spec).

The request below now constitutes a valid GetMap request:

::

    http://wms.example.com/wms?service=WMS&version=1.1.1&request=GetMap&layers=foo&srs=EPSG:4326&bbox=-180,-90,180,90&format=image/png&width=400&height=300&styles=default

Which is consistent with the WMS specification.

More information on these parameters can be found in the :ref:`wms_server` and
the `OGC WMS 1.1.1 specification
<https://portal.ogc.org/files/?artifact_id=1081&version=1&format=pdf>`__

For more detailed information, see `ticket 1088
<http://trac.osgeo.org/mapserver/ticket/1088>`__

.. warning::
    STYLES, though a required WMS parameter, is now optional again in
    MapServer. For more detailed information, see `ticket 2427
    <http://trac.osgeo.org/mapserver/ticket/2427#comment:2>`__

Using MapServer 6.0, why don't my layers show up in GetCapabilities responses or are not found anymore?
-------------------------------------------------------------------------------------------------------

MapServer 6.0 introduces the option of hiding layers against OGC Web Service
requests.  OGC Web Services can provide powerful access to your geospatial
data.  It was decided to disable layer level request access as a default.  See
:ref:`rfc67` provides a full explanation of the changes and implications.

To enable pre-6.0 behaviour, you can add the following to the :ref:`WEB` object's METADATA section in your
mapfile:

::

  "ows_enable_request" "*"

This will enable access of all layers to all OGC Web Service requests.

Where do I find my :term:`EPSG` code?
-------------------------------------------------------------------------------

There is a text file "epsg" in your PROJ4 installation (e.g.
"/usr/local/share/proj/epsg") which contain the EPSG information used by
PROJ4. In Windows, this is often located in C:\\proj\\nad or is found with an
environment variable called PROJ_LIB.

http://spatialreference.org allows you to search for EPSG codes.

You can also have a look at:
http://ocean.csl.co.uk

More information to EPSG:
http://www.epsg.org

More information to PROJ4:
http://trac.osgeo.org/proj

How can I reproject my data using ogr2ogr?
-------------------------------------------------------------------------------

With ogr2ogr of course! ogr2ogr is a powerful utility that will transform the
projections of your shapefiles when passed the appropriate parameters. In my
case, I was using MapServer to serve data in RI State Plane Feet. In order to
do so, the data had to first be converted to meters. Here is the command I
used:

::

    ogr2ogr -t_srs EPSG:32130 output.shp input.shp

Since my data already had a projection defined, I did not need to explicitly
state a source projection. This command uses the EPSG definition for NAD83
Rhode Island (32130) and performs the feet to meters conversion.

Now say my data wasn't already projected? Here's how we deal with that:

::

    ogr2ogr -s_srs "+proj=tmerc +lat_0=41.08333333333334 +lon_0=-71.5 +k=0.999994 +x_0=100000 +y_0=0 +ellps=GRS80 +datum=NAD83 +to_meter=0.3408 +no_defs" -t_srs EPSG:32130 output.shp input.shp

Let's examine what is going on here:

The -s_srs parameter explicitly defines a projection for the data. The
parameters used here were taken out of the EPSG definition (in this case,
32130) in the epsg file(see the `projection FAQ <epsg_codes>`__ for more
details on locating EPSG definitions). The entry for RI in the epsg file is as
follows:

::

    # NAD83 / Rhode Island
    <32130> +proj=tmerc +lat_0=41.08333333333334 +lon_0=-71.5 +k=0.999994 +x_0=100000 +y_0=0 +ellps=GRS80 +datum=NAD83 +units=m +no_defs  no_defs <>

You can see how the definition in the initial command is formulated. Notice
that the "+units=m" parameter has been changed to “+to_meter=0.3408”. This is
important for the conversion. Where did the value of 0.3408 come from you ask?
From the EPSG file! It has many goodies buried in it so by simply running
'grep "to_meter" epsg’ you can refresh your memory if you need to.

The next parameter in the command is "-t_srs EPSG:32130". This command tells
ogr2ogr to transform the data to the EPSG code of 32130. After this is
declared, all you need to do is declare a file name for your new shape file
and to set which file is being used as the input (note: make sure you don’t
confuse the order of these two).

Hit enter, bombs away, and enjoy your new data in meters!


How can I help improve the documentation on this site?
-------------------------------------------------------------------------------

New documentation material and corrections to existing documentation
are definitely very welcome. These contributions are handled through
the same issue tracker used to track software bugs and enhancements.

Follow the directions for submitting bugs at:
http://www.mapserver.org/development/bugs.html.
When creating a ticket, in the Component field, select `MapServer
Documentation`. If our ticket pertains to a specific web page, please
include the URL to that page.

If you have tips or examples that don't really fit the definition of
documentation, a good place to put them is the MapServer wiki at:
http://trac.osgeo.org/mapserver/wiki


What's with MapServer's logo?
-------------------------------------------------------------------------------

The MapServer logo illustrates the confluence of the `Minnesota`_ and `Mississippi`_ 
rivers, quite near to the home of the `St. Paul Campus`_ of the `University of Minnesota`_, which 
was the `birthplace of MapServer`_.

.. _`Minnesota`: http://en.wikipedia.org/wiki/Minnesota_River
.. _`Mississippi`: http://en.wikipedia.org/wiki/Mississippi_River
.. _`St. Paul Campus`: http://en.wikipedia.org/wiki/University_of_Minnesota#St._Paul_campus
.. _`University of Minnesota`: http://en.wikipedia.org/wiki/University_of_Minnesota
.. _`birthplace of MapServer`: http://lists.osgeo.org/pipermail/mapserver-dev/2009-December/009435.html