def get_geometry(lon, lat, size):
    """Returns a geo json geometry.
    
    Give lon, lat, and size in degrees.
    """
    geo_json_geometry = {'type': 'Polygon', 'coordinates': [[[lon - size / 
        2, lat - size / 2], [lon - size / 2, lat + size / 2], [lon + size /
        2, lat + size / 2], [lon + size / 2, lat - size / 2], [lon - size /
        2, lat - size / 2]]]}
    return geo_json_geometry
