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Publishing on the Public (Central) Web Server
Imagemaps: Server Side and Client Side
Discussion of server side and client side map differences excerpted from the
WebCom User Guide:
The standard methods for doing imagemaps on the Web have traditionally involved a three step process:
- The client clicks on a point on the image
- The coordinates of the point clicked upon are sent to the server.
- The coordinates are matched against a file containing the list of URls and co-ordinates (called a "map" file), and the URL
which is associated with those coordinates is returned to the client.
Step three sometimes involves running a script on the server. Because of the steps involved, imagemaps tend to be slower than
normal hotlinks, and use up much more system resources on the server.
Client Side Imagemaps are imagemaps which do not have to make a separate call to the server to determine what URL should be
returned to the browser. The coordinate/URL correlations are kept in the HTML coding of the page itself. After clicking on the
image, a request for the correct URL is immediately sent to the server, just as when a normal hotlink is clicked. This method loads
the page quicker, and uses less system resources in the process.
Another advantage of Client Side Imagemaps is that when the mouse pointer is held over sections of the map, the URL of the
destination page shows in the browser (In Netscape it appears at the bottom of the window) instead of just coordinates.
Apache Imagemaps
The Apache-specific imagemap documentation below is part of the documentation for the
imagemap module at http://www.apache.org/docs/mod/mod_imap.html.
Imagemap File
The lines in the imagemap files can have one of several formats:
directive value [x,y ...]
directive value "Menu text" [x,y ...]
directive value x,y ... "Menu text"
The directive is one of base, default,
poly, circle, rect, or
point. The value is an absolute or relative URL, or one
of the special values listed below. The coordinates are
x,y pairs separated by whitespace. The quoted text is
used as the text of the link if a imagemap menu is generated. Lines
beginning with '#' are comments.
Imagemap File Directives
There are six directives allowed in the imagemap file. The directives
can come in any order, but are processed in the order they are found
in the imagemap file.
base Directive
- Has the effect of
<BASE HREF="value">. The
non-absolute URLs of the map-file are taken relative to this value.
The base directive overrides ImapBase as set in a
.htaccess file or in the server configuration files. In the absence
of an ImapBase configuration directive, base defaults to
http://server_name/.
base_uri is synonymous with base. Note that
a trailing slash on the URL is significant.
default Directive
- The action taken if the coordinates given do not fit any of the
poly, circle or rect
directives, and there are no point directives. Defaults
to nocontent in the absence of an ImapDefault
configuration setting, causing a status code of 204 No
Content to be returned. The client should keep the same
page displayed.
poly Directive
- Takes three to one-hundred points, and is obeyed if the user selected
coordinates fall within the polygon defined by these points.
circle
- Takes the center coordinates of a circle and a point on the circle. Is
obeyed if the user selected point is with the circle.
rect Directive
- Takes the coordinates of two opposing corners of a rectangle. Obeyed
if the point selected is within this rectangle.
point Directive
- Takes a single point. The point directive closest to the user
selected point is obeyed if no other directives are satisfied.
Note that
default will not be followed if a
point directive is present and valid coordinates are
given.
Values
The values for each of the directives can any of the following:
- a URL
- The URL can be relative or absolute URL. Relative URLs can
contain '..' syntax and will be resolved relative to the
base value.
base itself will not resolved according to the current
value. A statement base mailto: will work properly, though.
map
- Equivalent to the URL of the imagemap file itself. No
coordinates are sent with this, so a menu will be generated
unless ImapMenu is set to 'none'.
menu
- Synonymous with
map.
referer
- Equivalent to the URL of the referring document.
Defaults to
http://servername/ if no Referer:
header was present.
nocontent
- Sends a status code of
204 No Content,
telling the client to keep the same page displayed. Valid for
all but base.
error
- Fails with a
500 Server Error. Valid for all but
base, but sort of silly for anything but
default.
Coordinates
0,0 200,200
- A coordinate consists of an x and a y value
separated by a comma. The coordinates are separated from each other
by whitespace. To accommodate the way Lynx handles imagemaps, should a
user select the coordinate
0,0, it is as if
no coordinate had been selected.
Quoted Text
"Menu Text"
After the value or after the coordinates, the line optionally may
contain text within double quotes. This string is used as the
text for the link if a menu is generated:
<a HREF="http://foo.com/">Menu text</a>
If no quoted text is present, the name of the link will be used
as the text:
<a HREF="http://foo.com/">http://foo.com</a>
It is impossible to escape double quotes within this text.
Example Mapfile
#Comments are printed in a 'formatted' or 'semiformatted' menu.
#And can contain html tags. <hr>
base referer
poly map "Could I have a menu, please?"
0,0 0,10 10,10 10,0
rect .. 0,0 77,27 "the directory of the
referer"
circle http://www.inetnebr.com/lincoln/
feedback/ 195,0 305,27
rect another_file "in same directory as
referer" 306,0 419,27
point http://www.zyzzyva.com/ 100,100
point http://www.tripod.com/ 200,200
rect mailto:nate@tripod.com 100,150 200,0
"Bugs?"
Referencing your mapfile
<A HREF="/maps/imagemap1.map">
<IMG ISMAP SRC="/images/imagemap1.gif">
</A>
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