This 1952 sci-fi novel takes place on the aptly named "Big Planet", a vast untamed world of high diameter and low density, where a lack of heavy metals impedes advanced technology. It has been settled by countless Earth colonies seeking the freedom to pursue their own particular way of life.
Earth authorities, concerned about the activities of a local warlord/slaver, send a team to investigate/intervene. However, their ship is sabotaged and crashlands on Big Planet. The survivors, led by Claude Glystra, set out on an impossibly ambitious trek to reach Earth Enclave, located on the other side of the planet, 40,000 miles away. Meanwhile, they continue to worry about the possibility of an enemy agent in their midst.
Although I like the idea of "Big Planet", I don't think Vance puts that idea to its best use here. The overarching warlord/sabotage plot tended to distract from the challenge of the planet itself, and tended to have the effect of making a big planet seem small again. Part of the problem, perhaps, is that Vance's original 1948 manuscript (now lost) was almost twice as long, but edited down after he was told it would not sell. But, for whatever reason, we are left with a rushed adventure story that could just as easily taken place on a small planet.
Vance's inventiveness is on display, but he has done better elsewhere. In particular, he has done better with his vastly superior 1975 novel SHOWBOAT WORLD (a/k/a THE MAGIFICENT SHOWBOATS OF THE LOWER VISSEL RIVER, LUNE XIII SOUTH, BIG PLANET), written 23 years later, which is also set on Big Planet. Read that one first - it stands on its own. Read this later, and only if determined to read all things Vance.
If you do seek out BIG PLANET, make sure you find an edition that reverts to the 1952 text that appeared in Startling Stories. The 1957 Ace edition, and later editions based on it (such as the 1977 coronet edition), massacred the 1952 text. The 2012 Kindle edition from Spatterlight Press, the Gollancz Kindle edition, 1978 Miller-Underwood edition (but not, as Wikipedia wrongly says, the 1978 Ace edition) and the unobtainable Vance Integral Edition revert to the 1952 text. I'm not sure about the Gollancz paperbacks. One test is whether the opening paragraph refers to Hidders' mixed-race origens and ends with a reference to "many brains". If so, then read on. If not, and if the second page refers to a "Sister of Succor" rather than a "nun", then hold off and wait for a better copy.