When someone tries to describe their family history to me (a distressingly frequent occurrence) the first thing I ask is whether they have a tree: looking at even the most complex of extended families laid out in the classic lines and boxes of a family tree instantly makes sense of distant relationships.

Hand-drawn trees are by far the most intelligible, but they have some serious drawbacks. First, they are fixed and, once complete, almost impossible to change. If you later discover a great-aunt Nelly and 40 third cousins, tough luck. Second, and more important, they can be extremely difficult to create, requiring a rare combination of research and graphic design skills. In fact I know of only one commercial family-tree artist in the country, Tony Hennessy of waterfordorigins.com.

The indefinitely revisable, computer-drawn tree usually suffices and, for better or worse, that now means online family trees. The three giants of commercial global genealogy, Ancestry, FindMyPast and MyHeritage now all offer well-designed trees that are potentially infinite. In the last two months the free Mormon site FamilySearch has also expanded and redesigned its service.

MyHeritage was originally a family-tree only site, free up to a certain number of ancestors, subscription thereafter, and now has the largest numbers worldwide. Ancestry’s de facto monopoly on North American research makes its online trees ubiquitous. But all use the same selling point. Invite great-aunt Nelly to examine your tree (for free) and she’ll correct all your mistakes about her family.

Just keep in mind the familiar warning about free internet services: if you’re not paying for it, someone else is paying to watch you.

What do I use myself? A twelve-year-old copy of FamilyTreeMaker, gloriously uncool and ugly and, most importantly, completely offline. My only online tree is locked up behind passwords and multiple administrator hierarchies on the paying-only tribalpages.com. Though I'm sure the NSA and the CIA know all about it.