самое главное, что кто их вкурил, в вики никаких пояснений не внес
внесли неясное: "When the footway has an occasional widening, e.g. when a number of ways meet, that can be mapped as a filled area by drawing a closed polygon, and adding area=yes. This area tag, however, should not be used to generally describe the shape or general width of a linear way, a few mappers use area:highway=footway in addition to the linear way for this purpose. "