@Override
        public ImmutablePair<String, Boolean> calculateMapAttribution(final Context ctx) {

            final StringBuilder attributation = new StringBuilder();
            for (ImmutablePair<String, Uri> mapUri : mapUris) {
                attributation.append("<p><b>").append(mapUri.left).append("</b>:<br>");
                attributation.append(MapsforgeMapProvider.getInstance().getAttributionFor(mapUri.right));
                attributation.append("</p>");
            }
            return new ImmutablePair<>(attributation.toString(), true);
        }
Create new render layer, if mapfiles exist
main/src/main/java/cgeo/geocaching/maps/mapsforge/MapsforgeMapProvider.java