The MAP element was first introduced in the Client Side Image Map
proposal (an HTML Working Draft from Spry.) It was very quickly adopted
in browsers and then in the HTML 3.2 recommendation. MAP is the
containing element of a grouping of shape-link identification pairs (the
AREA element) used to identify image map
linking destinations with geometric regions on an image. This is accomplished
via an HTML encoding system, rather than the older, more time consuming ISMAP
method which requires an extra HTTP request and server-side processing map file.
The Client-side image map model can be made backward compatible with the
old ISMAP model by specifying the USEMAP attribute in the
IMG element where an ISMAP attribute is also
present. The USEMAP attribute takes as its value the URL of a Client Side
Map specification. The URL specified can either be in the current or an
external file.
Description:
This attribute behaves the same as the A NAME attribute in defining
a destination within a document. It specifies the map location
within a file for reference by the IMG USEMAP attribute. They are
referenced in the IMG USEMAP attribute as either
"#mapname" [map is in the
current file] or "file/name#mapname"
[map location is in an external file] as appropriate.
Values: Non-null alphanumeric
strings under 256 characters in length.
It is usually a good idea to include an ISMAP as an alternative to
Client Side Image maps, but authors sometimes may not have access to
run binaries on their host machines. In this case especially, and in
general, a THIRD alternative should be authored to allow navigation
via text links for users that do not have image capability.
Browser Peculiarities
Netscape (even up to recent 4.0 Betas) does not allow the specification
of an external URL in the USEMAP attribute to the IMG element as per the
specification (only internal anchors can be used.) Internet Explorer
behaves according to the specification.