No one has suggested that the developers broke any laws, and the company that owns The Woodlands says it followed all applicable regulations and standards. But the experiences of the family of Ms. Martinez and their neighbors show that even when the mapping rules are followed to the letter, the results can be disastrous.

The adjustment process began as a way to correct the wild inaccuracies in the maps that form the basis of the federal flood-insurance program, which was created in the 1960s to protect homeowners from catastrophic loss. Increasingly, though, the changes have also become a way for developers to build on low-lying land.

Across the country, documents show, the Federal Emergency Management Agency, which runs the insurance program, has granted more than 150,000 map changes in the last five years. In some cases, lots were raised, and in others, levees, drainage systems, water-detention ponds and other methods changed the calculated flood risk for a swath of land.

Many of these changes were unquestionably appropriate. But in the Houston area, a Times analysis of FEMA documents shows, at least 6,000 properties in redesignated zones were damaged during the flooding caused by Harvey.

“This is all about engineers doing things for developers rather than for the public,” said James B. Blackburn, co-director of the Severe Storm Prediction, Education and Evacuation from Disasters Center at Rice University in Houston. Mr. Blackburn, who was involved in early designs of The Woodlands, added, “It would be nice to know that you were only two inches above the flood plain. You know, that’s not a lot of margin for error on these maps. Yet all the federal protection for flood insurance gets removed.”

What happened in The Woodlands underscored one of the great lessons of Harvey’s assault on Houston: the profound vulnerability of a metropolis with an ethos of untrammeled development built, essentially, on a swamp.

To Ms. Martinez and her neighbors, the cruel twist was that it could happen here — in a community founded in 1974 as a kind of anti-suburbia by an oil and gas billionaire named George P. Mitchell. If The Woodlands was a community apart, rich with woods, lakes, trails and streams, Mr. Mitchell was its benevolent dictator, whose vision of building quality and environmental balance fostered a reputation of a development where the flood risk was extremely low.