In 1975, the City of Gallup (defendant) signed an assessment procedure agreement (APA) with developers in a subdivision, including the predecessor in interest to Gallup Westside Development, LLC (plaintiff). The APA allowed for a development plan, subject to Westside and other developers complying with the terms of the APA. In 1996, Westside requested a site development review to develop the subdivision. The APA expired in 1995. The city created a letter agreement, extending the APA and amending it to be consistent with then-current building practices. Westside refused to sign the amended APA. Westside filed a different proposal to extend the APA, but the city’s Planning and Zoning Commission denied the proposal. The City Council affirmed this denial. Westside appealed to the district court, which reversed the city’s decision and issued a writ of mandamus directing the city to comply with the initial APA. The district court found that Westside had acquired vested rights in the subdivision. The city appealed.