Answered my own question I think; this link gives details of coverage of the city mapping, looks like it does what I'm after on the 605, the detail seems pretty good
http://www8.garmin.com/cgi-bin/mapgen/webmap.cgi?p=29425665&u=1&v=0&cp=7737585A5C69D85A&z=3&x=240&y=180&w=480&h=360&d=0&rz=0&k=1&sc=1
@marcomarcos started
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Answered my own question I think; this link gives details of coverage of the city mapping, looks like it does what I'm after on the 605, the detail seems pretty good
http://www8.garmin.com/cgi-bin/mapgen/webmap.cgi?p=29425665&u=1&v=0&cp=7737585A5C69D85A&z=3&x=240&y=180&w=480&h=360&d=0&rz=0&k=1&sc=1