When Web Map Tiles are constructed with, for example, wind arrows, the wind arrows may cross the boundary of the tile. Users and clients of the WMTS expect seamless, pixel accurate, joining of tiles. The 'overhanging' wind arrows may be truncated giving a misleading and messy map.

Even if a set of tiles are 'tuned' so that wind arrows do not 'overhang', the problem can re-occur when the map is zoomed, or the wind direction changes, or a different resolution of wind data is displayed.

This problem can also occur with other symbols representing features, or coverages, 'overhanging' the tile edges.

It is not clear how WMS, WMTS and SLD/SE should be changed to address this problem.

There are, of course, also performance issues with WMTS.

A more comprehensive description of this problem will be written with some possible options for progress.

-- ChrisLittle - 20 Jan 2010