Three points are enough to mark the location of any point on the surface of the earth. By analogy, any individual in a genealogical pedigree can be identified by having a minimum of three pieces of information (facts); a name, a date and the location of an event. Now, I realize that this is a very simplistic way of looking a what may be complex relationships, but the absence of any of the three basic facts results in an unacceptable degree of uncertainty.
For example, the lack of a name may make finding an ancestor difficult but not impossible. If you are attempting to move back in time and add another generation, the lack of a name, in the event of very common surname, may result in a complete inability to find the next generation of ancestors. Likewise, when dates disappear, so does the certainty of the identification of the ancestor. Dates can be estimated and names can be guessed, but a failure to find the place of an event can become the end of the line. How can you start looking for an ancestor if you have no idea where he or she lived considering the fact that nearly all genealogically useful documents are geocentric.
When beginning any genealogical research, it is absolutely necessary to understand the geography. I had a good example of this just this week. A patron at the Mesa Family History Center had accounts from various relatives that placed an ancestor back to a small town (a really small town) in Missouri. One document claimed the relative was born in Osage City, Cole County, Missouri. Another document said the relative was born in Osage County. Here was the problem. Osage County is right next to Cole County. The question was whether the location was Osage City or Osage County? So we looked at the map.
It turns out that Osage City is almost exactly on the border between Cole and Osage Counties. It is however, clearly in Cole County and almost next door to Jefferson City, the Cole County seat and the capital of the state of Missouri. Without consultation to a map, this problem would likely never have been solved. Looking at tiny Osage City, sitting just across the river from Osage County, clarified a number of issues, such as why the ancestors went to Jefferson City to get married.
I have said it many times, most of the so-called dead end or brick wall problems I hear about have their origin in a failure to adequately define the locations. The solution: look carefully at the maps and historic boundary changes. Do this first, before you get into a problem you cannot solve.