Two Sides To The Story (面 miàn and 边 biān)

I noticed something interesting about the way directions and sides are named in Mandarin.

Some of them have the suffix 面 miàn and some have the suffix 边 biān.

Examples of 面 miàn:

前面 qiánmiàn ("in front")

后面 hòumiàn ("behind")

里面 lǐmiàn ("inside")

外面 wàimiàn ("outside")

Examples of 边 biān:

旁边 pángbiān ("beside")

左边 zuǒbiān ("on the left")

右边 yòubiān ("on the right")

上边 shàngbiān ("on top")

下边 xiàbiān ("below")

北边 běibiān ("to the north")

南边 nánbiān ("to the south")

东边 dōngbiān ("to the east")

西边 xībiān ("to the west")

So why are certain directions or sides suffixed with 面 miàn and others suffixed with 边 biān?

A good explanation I found was on chinese.stackexchange.com. To reproduce it here (colouring mine):

To understand the differences properly, you need to know what is 面 and what is 边. 面 is a face whereas 边 is an edge. An edge is like a line guiding you [about] the direction. A face is what is facing you giving you a sense of position.

前/后面 is used to describe the position of something within your visual range. Whereas, 前/后边 is more appropriately used to describe something beyond visual range when giving directions.

镜子前面 (in front of the mirror) vs 车站前边 (beyond that bus stop in front)

外/里面 is used to describe location of an object in relation to another object. 外/里边 is used strictly for giving directions.

书包里面 (inside the school bag) vs 巷子里边 (in that alley)

左/右面 is used mainly to point to the left or right face of an object. 左/右边 is used to describe left or right side directions.

墙的左面 (on the left face of that wall) vs 车道左边 (left side of the roadway)

In summary, when you are giving directions, use 边; when you are describing positions, use 面.

I also found other explanations to the effect that the two terms were interchangeable, and it was more a case of regional preference (North China versus South China, or Mainland China versus Taiwan).

I'm not sure which explanation to believe, so I'm going to be conservative and stick to whatever Duolingo taught me, which is the initial list I provided.