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Re: Client Side vs. Server Side Image Maps

From: David Woolley <david@djwhome.demon.co.uk>
Date: Sat, 10 Feb 2001 12:14:52 +0000 (GMT)
Message-Id: <200102101214.f1ACEqp19754@djwhome.demon.co.uk>
To: w3c-wai-ig@w3.org
> The definition of the <a> element for IE5[1] doesn't list coords or
> shape as attributes. Since IE4+ is the most commonly used graphical

It may well be that IE is the one that is broken, rather than Amaya,
or as well as it.  However, IE tends to be the best commercial browser
with regards to standards; this has been in the standards for around
four years; and it ought to be easy to implement once you have support
for area.  In practice, image maps are so rarely used today that the
issue doesn't come up much.

It's one of those unfortunate facts of life that browser implementors
manage to break designs intended for graceful degradation on a regular
basis.  NS4 has effectively poisoned style sheets by making pages break,
rather than degrade to default presentation styles, when well structured
HTML is used with advanced styling - in particular, positioning.

(I don't know the exact history of client side maps, but it might well be
that they were introduced for the benefit of people with cheap web space
which didn't allow proper server configuration - meta is largely about this.
In that case, W3C may have made <a> elements an alternative to regain
accessibility but the browsers may not have followed.)

In practice, for image maps that are not fundamentally image maps++,
the next best thing to using text as text is to use a table to construct
a mosaic.  This works better on GUIs with images off than do real maps
(although I suspect its use is more to do with it commercial designers
finding it easier to understand, given their general disregard for
performance and insistence on images - mosaics are often done without
alt text, making it difficult to navigate before the image loads, which
is their main advantage on GUI browsers).

I think that WCAG requires that normal text links be provided outside
of the map, but regardless of this, if one is not penny pinching on web
hosting costs, one should provide a server side map which treats the
top left corner as a request for a text mode alternative.

In practice, modern text only browser can cope with area, provided you
provide sensible alt text (typically they construct a pseudo link to a
virtual page containing a menu from the map's alt text, or, in default,
the URLs) and old GUI browser will cope if you provide a server side map
a backup.  Browser that don't realise that they are dealing with an image
will not send coordinates, and ones that do, but are text only will send
0,0, which should be treated as a text only request.  Most servers will
ignore the coordinates if the rest of the URL points to a static resource.

++ fundamental image maps are ones where the geometric relationships are
of the essence of the navigation tool.
Received on Saturday, 10 February 2001 08:35:16 GMT

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