I\'m using the 1:50m Cultural Vectors shape file from naturalearthdata.com.
I use ogr2ogr to create a geoJson file with the following command:
ogr2og
What happens if you use the geoJson? For admin 0 level geographies like this (country level) a geoJson might suffice in terms of detail. It sounds like something is being lost when you go from geo -> topo?