What should be used as ALT text for a floorplan diagram?

W3C is a good place to start for HTML questions. The link below is their page about ALT. It tells people who can't see the picture what it is. So, "Floor plan of my house" or "floor plan of Buckingham palace" would do it. Someone who is REALLY interested will turn on his graphics, or ask a sighted person to describe it to him, or otherwise cope.

ALT should describe the graphic, not be the text equivalent. There is a difference. To take an extreme example, someone born blind who surfs with a browser that reads aloud to him is never going to know what a rainbow looks like.

ALT="Rainbow over pasture"

will tell him the picture is one of those rainbow things sighted people have been telling about all his life. You aren't going to be able to describe it to him.

Keep the ALT short, if there is useful information in the floor plan, write it up in a separate page, and link to it with the longdesc attribute. Newer versions of the JAWS screenreader, among others, should pick this up.

You should add the picture, (upload it to Flickr and copy the URL), and then ask this sort of question.

Well, my suggestion is that you just use alt="Floorplan". Keep it simple. ;)