it has been done ages ago, is called the maidenhead locator system, it is better in many ways, for example you can choose the granularity of the grid providing some privacy: https://en.wikipedia.org/wiki/Maidenhead_Locator_System

Numbers are not universal. In that 8 can be represented as Ⅷ, ב, ၇, 八 etc.

But I like your idea of a mapping system based on emoji :-)