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Enhance the label placement techniques so that you can optionally choose/configure a clipped geometry instead of the entire layer when finding label position. It would most likely be useful to be able to designate an arbitrary boundary so that the entire layer could be used, a boundary larger than the current map zoomed envelope, or the current map zoomed envelope could be used.
[jkemp101] May be useful to add another option that keeps labels from breaking across the defined boundary. This would allow tiles to be rendered using this option with out parts of labels being generated.
[springmeyer] This would be really cool. I wonder what functionality already exists in the feature query stuff though?
You can achieve this by doing sub-selects on your postgis geometries (if using postgis) in the mapfile or python syntax and then have your labels be associated this this sub-selected data as a new layer.
[springmeyer] see also #25 which also captures this idea.
text symbolizer in >= mapnik 2.2 supports 'clip' parameter