The image is a detail from a 1937 Home Owners' Loan Corporation red-lining map of Asheville. It is a photo of a copy of an original, so the color-coding is gone. Areas designated with a D were coded red, indicating highest risk. That usually meant there were African American residents, or some other "undesirable" group such as eastern European immigrants or in Asheville poor mountain immigrants. The principle held true in Asheville with at least one exception (see detail below): the area known as Shiloh in south Asheville, once exclusively and now largely African American, got C grade on this map, which would have earned it a yellow rather than a red code.
HOLC was a federal agency created in the Depression to manage foreclosures. By the mid-1930s it had developed a scheme to assess loan risks in neighborhoods across the country. In the HOLC rating scheme, an A designation was coded green and represented high value, new development, homogeneity, and room for more growth; a B was blue and indicated an area at its peak, fully developed; a C was yellow and meant it was an older area on its way downhill; and a D was red, which meant the housing was poor, dilapidated, with fewer owner occupants. The presence of African Americans tended to give an area a red rating, hence "red-lining." Needless to say it was difficult if not impossible to get a loan for a house in a red area.