I have been working the southwest area of Morgan Hill, California for the last few weeks and I have noticed a serious problem with the map renderers -- Mapnik, Osmarender, etc. Changes to streets take days to show up, or never show up. I go back to JOSM and check the database, and the changed data appear to be correct, but the renderers never pick them up. Even worse, the presentation varies by zoom level. I see streets and other features that have had their properties changed days earlier, and at certain zoom levels old data still persist. I'm assuming these are problems with the rendering algorithms, and not the underlying database. However, since most site visitors will see the map as a rendered presentation of the database, it seriously limits the usefulness of OpenStreetMap at present.

The weird lag or lack of proper rendering by zoom level seems to imply that the renderers are making multiple passes to render changes for a region and are somehow being interrupted in that task before all zoom levels have been covered, so the changes never show up to the end user. Perhaps this could be fixed, at least in the short term, by allowing editors to select a region, say, 1 km square or smaller, or select a specific way, and manually force the renderers to update views at all zoom levels within the box or length of the way. This could be handled as a queued background task, so as not to bog down the servers excessively.