The world of ''The Sharing Knife'' is post-post-apocalyptic, as in gone back to nature, mostly. The major river from ''Passage'', the Grace, has been compared to the Ohio river in [[WordOfGod author notes]], which is a tributary to the idenitically-laid-out Gray/Mississippi river. The big dead lake on the north end of most maps was said to have once been a chain of lakes, with 'straight' roads around them made by the sorcerer-lord Precursors. I keep coming back to the suspicion that this world is actually the post-apoc version of the North American Midwest, around about Ohio and Indiana. The Ogachi Strand is the ruins of Chicago, and like other modern major cities, was easily several miles across. Michigan is buried in the crater of the Dead Lake, or was destroyed in the blast that merged the Great Lakes. The malice-blight is easily seen as a form of radiation, leeching life-energy from the land. Lakewalker magic is easy to justify, depending on your favored flavor.
* The techno-method has it as wireless-linked nanotechnology which has infiltrated and permeated all matter harmlessly, which the Lakewalkers use inherently. (I hate DoingInTheWizard, personally, but it's there.)
* Or they really DID discover a 'magic' or supernatural/psionic ability/power. (Maybe it's even an alternate-world history, with magic overtaking science in the Renaissance, but inaccessible to Farmers.)
** I thought this was canon, honestly. The map of the world looks like North America and they mention legends of lands across the seas if you could only get a big enough ship to sail that far, they talk about a big war that melted the miles-wide cities into glass craters (nuclear bombs), some of the highways are made of strange black rock that is all one piece and doesn't erode (asphalt)... I entirely agree with you, and I think it's the author's intention.