Hi, Could I suggest you add the &srs=3857 to the URL when you request the tile specs here: https://api.os.uk/maps/vector/v1/vts?key=XXXXX&srs=3857 So the API would appear like this: "https://api.os.uk/maps/vector/v1/vts/tile/{z}/{y}/{x}.pbf?key=XXXXX&srs=3857" That would avoid having to make a transformRequest for each tile and I think it's safe to assume the user wants the tiles in that SRS. Thanks