Urban expansion is a pivotal issue in emerging markets and developing countries, with Ulaanbaatar, Mongolia's capital, exemplifying this challenge. Home to half of the country's population, Ulaanbaatar faces significant pollution and overcrowding issues, largely due to the ger district, characterized by traditional Mongolian tent houses ('Gers') and insufficient infrastructure. This research uses various data sources to analyze the city’s historical morphology and population changes from the 1990s to 2020, with a particular focus on the ger district. Using the Global Human Settlement Layer (GHSL), crowd-sourced data, and governmental census data, we analyze Ulaanbaatar's settlement expansion and population changes from 1990 to 2020. Our approach introduces city-wide and 'Ger District' comparisons, supplemented by district-level analysis to capture the city's heterogeneity. We employ the United Nations (UN) Sustainable Development Goals (SDG) 11.3 index, specifically the Land Consumption Rate to Population Growth Rate (LCRPGR), to assess these changes. Our findings indicate that Ulaanbaatar's overall population growth peaked from 2000-2010, but the ger district's growth rate saw a surge from 2010-2020. This increase significantly expanded the city's total settlement footprint, leading to high land consumption rates (LCR) during this period. The low-density expansion is notably reflected in the city-wide LCRPGR index, with values exceeding 1 from 2010-2020, a significant rise from earlier periods. Our study highlights the necessity for a nuanced approach to urban expansion analysis, considering both city-wide and district-level dynamics. The insights gained are invaluable for urban planning and sustainable development strategies in Ulaanbaatar and other rapidly growing cities.