Most people are broadly aware that housing is more expensive in politically liberal coastal metro areas, but the full extent of the alignment is striking. Here's a scatterplot from Jed Kolko at Trulia:
You can see that the driver of the trend isn't that all liberal cities are expensive. Plenty of them are cheap. But only one red market — Orange County — is expensive, and it's not that conservative. One reason houses are more expensive in these cities is that incomes are higher, but as Kolko writes "those higher incomes are not enough to offset higher home prices" and middle class buyers end up with less affordability on the coasts despite the higher incomes.
These expensive blue areas are generally the most densely populated in the country already, but the only durable fix for the affordability crisis is to change zoning to allow for even more density.