The URI is correct. The /wiki/ URL is a description of the map, but not the canonical URI of the map itself (comparable to the difference between http://www.wikidata.org/entity/Q42 and https://www.wikidata.org/wiki/Q42). The only problem is that the redirect from the canonical URI to the description isn’t live yet: see T163922: Create a URL rewrite to handle the /data/ path for canonical URLs for machine readable page content.

(Side note: the redirect goes to Special:PageData, not directly to /wiki/Data:…, just like Wikidata /entity/ URIs redirect to Special:EntityData and not directly to /wiki/… – the special page does content negotiation, and (with appropriate Accept headers) gives you the actual data directly.)