'Render a single tile, return a Response instance.'

def renderTile(self, width, height, srs, coord):

    try:
        query = self.queries[coord.zoom]
    except IndexError:
        query = self.queries[(-1)]
    ll = self.layer.projection.coordinateProj(coord.down())
    ur = self.layer.projection.coordinateProj(coord.right())
    bounds = (ll.x, ll.y, ur.x, ur.y)
    if (not query):
        return EmptyResponse(bounds)
    if (query not in self.columns):
        self.columns[query] = query_columns(self.dbinfo, self.srid, query, bounds)
    if (not self.columns[query]):
        return EmptyResponse(bounds)
    tolerance = ((self.simplify * tolerances[coord.zoom]) if (coord.zoom < self.simplify_until) else None)
    return Response(self.dbinfo, self.srid, query, self.columns[query], bounds, tolerance, coord.zoom, self.clip, coord, self.layer.name(), self.padding)
