The National Archives holds one of the largest and most important accumulations of maps in the world. They document the United Kingdom's involvement in shaping boundaries and in resolving boundary disputes over many centuries, either as a colonial power, neutral observer or independent source of surveying expertise. Rose Mitchell looks at how the process has been documented, from letters and reports to treaties, drawing on maps and surveys which made lines across sand, snow, water, forests, plains and mountains around the globe.Rose Mitchell is a map curator at The National Archives. She is co-author of Maps: their untold stories.