Andrew has just pushed an update to the summits site for the GI association.
Previously we has the same Bing link in place for all G* associations, but the OSGB mapping held by Bing does not cover GI. The button has been replaced with a new link to OSNI mapping:
When you land on OSNI’s map viewer it gives you a default map which is no so useful for hiking. Click on the base-map button:
This will pop up a selector - the 1:25k and 1:50k layers are good to explore. Be prepared to zoom in and out for best results.