Urban settlements along the US and Mexico border are some of the fastest growing regions in each respective country. This project imagines an east west megalopolis, similar to those currently spread North/South along the coastal United States. By manipulating the space of the border through elongation and compression, various relationships become apparent. In collapsing the string of “sister cities” occurring along this divide, patterns of development and urban form are juxtaposed, highlighting differences and similarities and suggesting future routes of growth. The area between each respective sister city and the border becomes activated as a space of potential connectivity. By analyzing how each urban form addresses the border, either by pushing up against it, even using it as quotidian infrastructure, or by pulling back, creating an additional buffer between the two nations, various characteristics and typologies appear. In the case of El Paso and Ciudad Juarez, and other similarly sized metrapoles, the two border populations have veritably collapsed, with the border practically dissolved by the daily bustle. In smaller cities such as Columbus, New Mexico and Puerto Palomas, Mexico, a gap of three miles exists between the two cities, yet because of the strong reciprocity and interdependence between the two communities, this space is evaporated; the border fence being a weak demarcation of differences not observed. In other instances, such as Sullivan City and Ciudad Gustavo Diaz Ordaz, the proximity of larger urban centers diverts the exchange that would otherwise exist between these two adjacent cities. Every sister city relationship has unique characteristics shaped by local history, industry, geography and location in the larger map, yet in each instance, the space that defines the border in between is charged and presents opportunities for analysis and methods for responsible and just exchange.