I'm planning to create an online map with openlayers (2 or 3) or leaflet. I have to show some points/markers (~30.000), polygons (~500) and lines in an area of ~10x10 kilometers in several layers. This data comes in local x and y coordinates. The background will be made of raster tiles, perhaps OSM.
Now I'm wondering, whats the best strategy to do this.
Is it possible to make the local coordinate system the default for the whole map in one of those map libraries?
If not, should the data be converted into the coordinate system of the map (WGS 84) in the database or a cache or doesn't that matter?