def dimension_values(self, dimension, expanded=True, flat=True):
        """Return the values along the requested dimension.

        Args:
            dimension: The dimension to return values for
            expanded (bool, optional): Whether to expand values
                Whether to return the expanded values, behavior depends
                on the type of data:
                  * Columnar: If false returns unique values
                  * Geometry: If false returns scalar values per geometry
                  * Gridded: If false returns 1D coordinates
            flat (bool, optional): Whether to flatten array

        Returns:
            NumPy array of values along the requested dimension
        """
        values = []
        found = False
        for el in self:
            if dimension in el.dimensions(label=True):
                values.append(el.dimension_values(dimension))
                found = True
        if not found:
            return super(CompositeOverlay, self).dimension_values(dimension, expanded, flat)
        values = [v for v in values if v is not None and len(v)]
        if not values:
            return np.array()
        vals = np.concatenate(values)
        return vals if expanded else unique_array(vals)