Within administrative regions, urban built-up areas are vast stretches of constructed areas equipped with basic public facilit ies. Human act ivit ies most frequently take place within urban regions and the dynamic evolution of urbanization has caused profound variations in urban spatial structures. Conventional boundary extraction methods are complicated and require human intervention. This article innovatively proposes a vector method that combines a data-dimension compression index known as an Index-based Built -up Index (IBI) with aggregate analysis to extract vector boundaries of urban built-up areas automatically by setting a threshold value and the parameters for aggregate analysis. Datadimension compression technology is used to extract urban built-up areas using thematic bands (rather than original bands) to build indexes, which improves the precision of extraction. Areas ext racted by the methods above contains urban built-up areas, rural built-up areas, independent houses and fully bare areas. Aggregate analysis aggregates a certain range of non-adjacent plots into a new polygon section. This method has made it easy to analyze the spatial expansion of Wuhan city from 2003 to 2013. This method avoids cumbersome process es of outlining vector boundaries by artificial visual interpretation with a better working efficiency and reduced costs than other methods, which cannot accurately determine vector boundaries to an accurate degree by manual vector quantizat ion without depending on other data or expert knowledge. Compared with t raditional boundary extraction methods, this vector method is more efficient, precise, objective, and exquisite.