To reproduce: The TileSize property of the LocalMapProvider is readonly.

Workaround:

 public class CustomLocalMapProvider : LocalMapProvider
        {
           
            public CustomLocalMapProvider()
            {
              
                FieldInfo fi = typeof(LocalMapProvider).GetField("tileSize", BindingFlags.Instance | BindingFlags.NonPublic);
                fi.SetValue(this, new Size(200,200));
            }
        }