Maps have long played a crucial role in enabling people to conceptualize and navigate the world around them. How-ever, maps also encode the world-views of their creators. Disputed international borders are one example of this: gov-ernments may mandate that cartographers produce maps that conform to their view of a territorial dispute. Today, online maps maintained by private corporations have become the norm. However, these new maps are still subject to old debates. Companies like Google and Bing resolve these disputes by localizing their maps to meet gov-ernment requirements and user preferences, i.e., users in dif-ferent locations are shown maps with di-erent international boundaries. We argue that this non-Transparent personaliza-tion of maps may exacerbate nationalistic disputes by pro-moting divergent views of geopolitical realities. To address this problem, we present MapWatch, our sys-tem for detecting and cataloging personalization of inter-national borders in online maps. Our system continuously crawls all map tiles from Google and Bing maps, and lever-ages crowdworkers to identify border personalization. In this paper, we present the architecture of MapWatch, and ana-lyze the instances of border personalization on Google and Bing, including one border change that MapWatch identified live, as Google was rolling out the update.