The canton Basel-Stadt has its own aerial imagery that it updates roughly every 2-3 years, the current version is from April 2015, for whatever reasons the imagery doesn't seem to have been included in any of the lists used by the OSM editors up to now. I'm in the process of changing that after I checked with the cantonal GIS department that the imagery can indeed be used for our purposes, if you want to use the imagery in iD right now, you can use the following link in the custom imagery configuration:
http://mapproxy.osm.ch:8080/tiles/KTBASELSTADT2015/EPSG900913/%7Bz%7D/%7Bx%7...
The coverage extends in to Germany and France
http://mapproxy.osm.ch:8080/demo/?tms_layer=KTBASELSTADT2015&format=png&...
and may be of interest to mappers there too (crossposted to talk-de).
Simon