President Assad's forces have reported to have cut the narrowest point of the rebel held area to just 500 meters across.

据报道，总统阿萨德的军队与叛军控制地区最近距离只有500米。

" Radius" , " diameter" , full length, basically cutting it in half, equal points.

“半径” ，“直径” ，全长，基本上把它切成两半， 等分。

That wouldn’t be as viable if the square had, say, 24 cut points, but with just 8 there are only so many reasonable options.

如果正方形有 24 个切点， 那将不那么可行，但只有 8 个切点， 合理的选择就这么多。