def get_coordinate_system(self):
        """
        Check self.Data for available coordinate systems.

        Returns
        ---------
        initial_coordinate, coordinate_list : str, list
        i.e., 'geographic', ['specimen', 'geographic']
        """
        coordinate_list = ['specimen']
        initial_coordinate = 'specimen'
        for specimen in self.specimens:
            if 'geographic' not in coordinate_list and self.Data[specimen]['zijdblock_geo']:
                coordinate_list.append('geographic')
                initial_coordinate = 'geographic'
            if 'tilt-corrected' not in coordinate_list and self.Data[specimen]['zijdblock_tilt']:
                coordinate_list.append('tilt-corrected')
        return initial_coordinate, coordinate_list