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</o:shapelayout></xml><![endif]--></head><body lang=EN-GB link=blue vlink=purple><div class=WordSection1><p class=MsoNoSpacing>To OSM vector map-makers: do we need the 1:1 vector geometry on the map server?<o:p></o:p></p><p class=MsoNoSpacing>To be short I need to jump over many, many fine details. Yet I believe that for most of the related notions and processes we have approximately the same understanding. Anyway, in the vector geometry data preparation one of the essential processes is the scale-levels generation. This phase is about the end of the preparation chain, just before the (global) tiling.<o:p></o:p></p><p class=MsoNoSpacing>I am intentionally using the scale-level notion instead of zoom-level because the criteria – when and the model – how to create the scale-levels is considerably different compared to the similar raster map-making processes. For when, I use the data amount criterion (for now 11 levels) and for how, I use a vector smoothing and data reduction model (sometimes called data-generalisation). In this way for arbitrary scale factor the data amount to transmit from server to a client is between 2 – 8 KB per km**2 equivalent (for about 50 area and line OSM object classes). And here is my point:<o:p></o:p></p><p class=MsoNoSpacing>In the vector mapping systems the start scale-level Lev0, created with the scale factor 0.001 (1:1000), just perfectly replaces the 1:1 geometry. This means that rendering/displaying the source 1:1 geometry over the geometry from Lev0 (or the contrary) you will not see any differences on a 120 dpi display surface. Eventually, you may exceptionally see one pixel difference using high scale values like 1/200 or 1/300. But what is important that is the data amount. Lev0 contains for about 15% less nodes/points compared to the 1:1 level for the mentioned 50 object classes. In other words, using Lev0 in scales between 1:200 and 1:5000, the server could handle about 426.5 million points/vectors less (compared to a bit more than 2839.3 million vectors in 1:1 geometry). Of course this has impact on the transmission and client rendering efficiency as well.<o:p></o:p></p><p class=MsoNoSpacing>Thanks for the comments, Sandor.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p></div></body></html>