While it is possible for a pyramid to have a square bases, you should not assume that all pyramids have square bases. Try to picture a triangular pyramid in your head, hopefully you can see that it is possible, and this would answer your question.
A square-based pyramid has, let's see, a top vertex, and 4 vertexes on its base (the part in the ground) for a total of 5 vertexes.
An age structure graph, also called a population pyramid, is a graphic description of the age and sex group distribution in a country's population. Please see the link for details.
look at "how do you make a pyramid?" to see
Yes, the Great Pyramid of Giza is a square pyramid. From a birds eye view, you could see that the bottom is in the shape of a square. See: http://www.mathsisfun.com/geometry/pyramids.html
Trough the 'common sense' theory of the least effort: to build a pyramid, it had to be erected trough many ramps that allowed to carry heavy weights to the top of the pyramid, using the least effort. See related links for some examples.
See link regarding population centers. This may give you enough to calculate what you need.
yes
Around 28 millions (97 % of total population) per Pew Forum study as of October 2009. See link below.
So that other people can see how a pyramid can have art in it.
Great pyramid are visible from far because of their massive size. Cairo Tower and el Citadel are the two places from where you can see the Great Pyramid.
a pentagon if you need to see a picture google pentagonal pyramid