Why does each link in the results cover a random number of cities?

In the Direct Results, why do some links cover 11 cities, while others cover 25?  Why is only part of my state included in a link, with the rest in a separate link?  Why not just put everything together?

Basically the reason is because of how craigslist organizes their results.  From any given craigslist city, you can search a number of nearby cities (up to 30, within a range of 200-300 miles).  So, we worked out the most efficient way to 'tile' the entire country in these regions so that everywhere is covered.  For larger states like California or Texas (and a few others) the state is simply too big to fit it all together under one link.  In other cases, a whole state could fit in one link, but we split it up to reduce the total number of links.  For instance, there might be three states beside each other, and instead of putting each under its own link, we split the middle one in half, so you only end up with two links instead of three.

As a result of these little optimizations, we're able to cover the entire country in just over 20 links (all of which can be opened at once using the 'Open All' button.  However, if you prefer to give each state its own link, you can switch the grouping from by 'area' to by 'state', using the dropdown box just above the results links.  That will result in more links overall, but will group entire states into a single link where possible.