Perhaps I could have been more precise but what I meant is if you look at the chart at some time in your flight prior to getting to the grid square in question.....the large blue two digit number will indicate the highest elevation/obstacle height given as MSL and one can immediately arrive at a "safe" altitude to fly.
I suppose we could throw in comments about the difference between mountainous and non-mountainous terrain and how the "safe" height above each vary from the other.
This excerpt from a usually reliable source explains how those numbers are derived.
All sectionals and terminal charts contain Maximum Elevation figures in each latitude and longitude box. They are stated in thousands and hundreds of feet above mean sea level (MSL). They represent the highest obstacle (towers, terrain, antennas etc.) within the box, with usually a 100 ft. error allowance added, and then rounded up to the next 100 ft. level.
In reality, what I should have said is one could look at the map and deduce those altitudes that would pose a danger to safe flight.
Perhaps someone can explain how to compute actual altitude vice indicated altitude so we can all be completely safe out there.