Of course, visiting the whole world takes a lot of time. So, in any point in time, there are sites and cities I've already visited... and there are some in the future, either in the next weeks... or in the next few years.
There are several levels of planning required for such adventure. The first level is to determine globally where you'll go. In my case, it's the sequence of continents I'll visit. I'm starting with North-America, then Central and South Americas before crossing to Europe (I will look at the possibility to go in Antartica, but not officially in my plans for now). Then, it will be Africa, Asia and Australia before returning to North America.