It depicts the gender ratio in each county at different points in the age range. So you see that most children are boys, while most senior citizens are women. Men die younger, in other words, but that's offset by the fact that there are more newborn boys than newborn girls. In the middle brackets, however, there seems to be a marked tendency for women to outnumber men on the east coast while men predominate on the west. Women also appear to be more concentrated in urban areas than men, perhaps because rustic occupations tend to be disproportionately male while women are disproportionately likely to work in the very urbanized health care sector.