Usefulness of simplifying models (re-posted due to a technical problem)

Tomorrow at the colloquium, we will be discussing Sarah Lawsky's paper, "Modeling Uncertainty in Tax Law." More on this in due course. But as the paper discusses, among other topics, the question of what makes a model useful - in particular, the tradeoff between being complete on the one hand and usable on the other - I was reminded of a favorite quote, from Lewis Carroll's Sylvie and Bruno Concluded:

“That’s another thing we’ve learned from your Nation,” said Mein Herr, “map-making. But we’ve carried it much further than you. What do you consider the largest map that would be really useful?”

“About six inches to the mile.”

“Only six inches!” exclaimed Mein Herr. “We very soon got to six yards to the mile. Then we tried a hundred yards to the mile. And then came the grandest idea of all! We actually made a map of the country, on the scale of a mile to the mile!”

“Have you used it much?” I enquired.

“It has never been spread out, yet,” said Mein Herr: “the farmers objected: they said it would cover the whole country, and shut out the sunlight! So we now use the country itself, as its own map, and I assure you it does nearly as well."

It turns out that Lawsky also knows this quote, and indeed cited it in an earlier article. (See pp. 1673-74 at n. 95.)

Silly me, I had originally thought that the full-sized map idea must be from Gullver's Travels, perhaps the visit to Laputa, but couldn't find it there via Project Gutenberg, whereupon I opened up broader inquiries and was soon set right.

Sylvie and Bruno, by the way, is a startling mixture of the sublime with the excruciating. It's richly studded with bits that anyone who loves the Alice books should find comparably delightful, mixed with sickening treacle as well as the comparatively mundane. But nonetheless a must-read for any Lewis Carroll fan (and I rate the Alice books pretty much at the pnnacle).

UPDATE: I can't resist one more Lewis Carroll quotation about maps, this time from The Hunting of the Snark:

He had bought a large map representing the sea,
Without the least vestige of land:
And the crew were much pleased when they found it to be
A map they could all understand.
“What’s the good of Mercator’s North Poles and Equators,
Tropics, Zones, and Meridian Lines?”
So the Bellman would cry: and the crew would reply
“They are merely conventional signs!
“Other maps are such shapes, with their islands and capes!
But we’ve got our brave Captain to thank:
(So the crew would protest) “that he’s bought us the best —
A perfect and absolute blank!”
This was charming, no doubt; but they shortly found out
That the Captain they trusted so well
Had only one notion for crossing the ocean,
And that was to tingle his bell.