Alt text for maps, floor plans, and campus diagrams

It's orientation week and somebody posts the campus map. Sixty buildings, four parking lots, a star on the student center, a legend set in six-point type. The image description reads "Campus map." For a student using a screen reader, that's the whole thing: there is a map, it is of campus, good luck.

Maps are the hardest images to describe, and the reason is structural rather than a matter of effort. The W3C's images tutorial groups maps, diagrams, and charts together as complex images — images carrying more information than a short phrase can hold — and says they need a two-part text alternative: a short description that identifies the image and points to where the detail lives, plus a longer description that actually carries the information. So the question was never "how do I compress a floor plan into one sentence." It's "what is this map for, and where does the real answer go?"

Name the purpose before you describe the picture

Almost no map needs to be described as a map. A reader wants one of about four things from it: how to get somewhere, where an event is, which building holds what, or how a space is laid out. Write to the thing they came for. That's the same instinct behind why alt text matters in the first place — you are replacing what the image does, not narrating what it looks like.

A parking map exists to say where to park. A floor plan on an event page exists to say the ballroom is on level two, past the elevators. Once the purpose is named, the alt text gets short — often well under the 125-character guideline.

The detail belongs on the page, not in the attribute

The long description is the part teams skip, and it's the part doing the work. W3C shows three ways to attach one: a text link beside the image pointing to the full description, a note inside the alt attribute saying where that description is, or a figure element wrapping the image and its description together as one unit.

WebAIM puts the practical version plainly: when an equivalent won't fit in a succinct alt attribute, put it somewhere else — an adjacent list, a data table, a linked page — and let the alt attribute describe the general content of the image. It's the same division of labor as describing charts and infographics, where the alt names the thing and the text nearby carries the numbers. One approach to skip: longdesc is deprecated and was never well supported, so don't reach for it.

On social, the caption is your long description

Social platforms hand you an alt field and nothing else. There's no adjacent table to point at and no description page to link. So the split moves: the alt field says what the map is and what it shows, and the caption carries the address, the room number, the parking instruction. Your sighted followers are pinching and squinting at that legend too, so this is rarely wasted effort — it's the reflex we recommend to SnipAlt for college teams pushing wayfinding graphics out during move-in.

The exception is worth stating. If the map is scenery — a stylized world map behind a headline, a decorative floor-plan texture on a slide — then marking an image decorative is the honest answer, not a shortcut.

Clickable maps have twice as many fields

If your map is interactive on the site — an HTML image map with a hotspot per building — there are two layers to fill in, not one. W3C's image map guidance is that the image itself needs a text alternative conveying the informative context, and every clickable region needs its own alt text naming where that link goes. Skip the second layer and a keyboard user tabs through a row of unlabeled links, which is worse than a static picture would have been.