# Shapely's simplify won't simplify any more

I have a multipolygon in shapely, and I want to simplify it until it has less than a certain number of points. When I use the `preseve_topology=False` argument to `geom.simplify`, I can get the number of points arbitrarily low.

However if I leave that out (i.e. `preserve_topology=True`), there appears to be a hard limit of how much it will simplify the object. As I increase the parameter (and hence make it "more simple"), the number of points stays stuck.

`gg` is a MultiPolygon with 255726 points in Google Mercator projection (EPSG:3857).

With preserve_topology=False:

``````(Pdb) pp [(10**i, i, num_points_in_polygon(gg.simplify(10**i, preserve_topology=False))) for i in range(1, 20)]
[(10, 1, 134598),
(100, 2, 27531),
(1000, 3, 2523),
(10000, 4, 156),
(100000, 5, 13),
(1000000, 6, 0),
(10000000, 7, 0),
(100000000, 8, 0),
(1000000000, 9, 0),
(10000000000, 10, 0),
(100000000000, 11, 0),
(1000000000000, 12, 0),
(10000000000000, 13, 0),
(100000000000000, 14, 0),
(1000000000000000, 15, 0),
(10000000000000000, 16, 0),
(100000000000000000, 17, 0),
(1000000000000000000, 18, 0),
(10000000000000000000L, 19, 0)]
``````

With default preserve_topology=True:

`````` (Pdb) pp [(10**i, i, num_points_in_polygon(gg.simplify(10**i))) for i in range(1, 20)]
[(10, 1, 135174),
(100, 2, 32572),
(1000, 3, 10947),
(10000, 4, 8760),
(100000, 5, 8519),
(1000000, 6, 8509),
(10000000, 7, 8509),
(100000000, 8, 8509),
(1000000000, 9, 8509),
(10000000000, 10, 8509),
(100000000000, 11, 8509),
(1000000000000, 12, 8509),
(10000000000000, 13, 8509),
(100000000000000, 14, 8509),
(1000000000000000, 15, 8509),
(10000000000000000, 16, 8509),
(100000000000000000, 17, 8509),
(1000000000000000000, 18, 8509),
(10000000000000000000L, 19, 8509)]
``````

As you can see, it stubbornly stays at 8509 points, even with a massive simplification param.

Is this sensible? Is there a bug in shapely/geos? Is there a way to simplify, and preserve topology and get arbitrarily simple objects?