To meet the challenges of climate change, cities, which in the U.S. are responsible for about 60% of total national energy consumption, are trying to determine how they can achieve deep carbon reductions.  However, they often the lack the data and analysis to determine the most optimal path for achieving their goals.  Using the case study of the District of Columbia's climate and energy plan, called Clean Energy DC, as well as using hourly energy consumption modeling for the buildings in the District of Columbia to help make energy and utility investment decisions to optimize energy resources, both of which I led the efforts on, I'll present ways of using existing data and planning analysis to priortize investment decisions and to develop an optimal roadmap to decarbonization.  I'll present excerpts from Clean Energy DC, Assessing the Potential of Neighborhood-Scale Energy Systems in DC, as well as clean energy plans from Seattle and Boulder, CO.