According to Success Criterion 1.1.1 (Non-Text Content), all client-side image maps, using the map element, should have alt text (a short-text alternative) for each of its constituent area elements.
This example demonstrates an image map with two areas, both containing alt elements as specified. A notice is emitted to remind authors of the responsibility of ensuring the contents of the area element "serves the same purpose as the part of image map image referenced by the area element". In this example, these alternatives are probably not adequate.