The project for the proposed Large Synoptic Survey Telescope (LSST) performed more than two years of data
collection, site evaluation, and analysis to support the selection of its prime site. LSST assessment was based on
using an existing site with existing infrastructure and historical performance information. A large and diverse set of
comparative information was compiled for potential sites using results from other site campaigns, measurements
from existing large telescopes, new astro-climate measurements, logistical and feasibility information, and from
existing satellite and climate databases. Several analyses were performed on these data including the assessment of
survey performance using the LSST operation simulator. An independent site selection committee of experts
provided recommendations to the Project leading to three finalist sites, one in Mexico, and two in northern Chile.
The finalist sites were assessed thoroughly with additional data collection from all-sky cameras and site proposals.
Cerro Pachon in Chile was selected to be the site for LSST after a difficult decision between the high quality final
candidates. This paper describes the data, analysis and approach used to support the site evaluation.