The map above this post shows the world divided up into 28 million 3x3mile squares. If the square has a population of 8,000 people living within it (and therefore a population density 889 people per square mile) then the square is coloured yellow. If it has less than 8,000 people living within it then it is left black. Thus the yellow areas are the most densly populated areas of the world, the dark areas are less densly populated. The numbers have been chosen by the map's designer Max Galka from population data compiled by NASA so that half of the world's population lives within the yellow parts of the map, and the other half lives within the black part of the map. (Go here for his blogpost and some close up details of the map.)
Of course the picture is necessarily simplified, there is no differentiation for the greater population densities: the population density of Manhattan is about 67,000 people per square mile, while in the centre of Cairo over a million people live within 9 square miles. But the picture does show that a lot of us in the world live in very close proximity with others. In fact half of us live on 1 percent of the world's land (the yellow bits)! Thus, there are plenty of wide open spaces out there in the world, but we tend to prefer to visit those places for a holiday rather than live there...