Every time your phone tells you where you are, it is using a mathematical model of the shape of the Earth. A Black woman from rural Virginia spent decades building that model by hand, and almost nobody knew her name until she was in her eighties. Gladys West. She grew up in a sharecropping family in Dinwiddie County and understood early that the alternatives were the tobacco fields or the factory. She finished top of her high school class, which came with a scholarship, and took it. Her work was satellite geodesy: taking the raw data coming down from orbit and using it to compute, correction by correction, the true irregular shape of the Earth. Not a sphere. Not even a neat ellipsoid. A lumpy thing with gravitational highs and lows. That model is the foundation the Global Positioning System sits on. You cannot locate a point on a surface until you know precisely what the surface is. She did this for decades, largely unremarked, and retired in 1998. She was recognised in 2018, when her sorority mentioned her biography at a function and someone realised what was in it. The Air Force inducted her into its Space and Missile Pioneers Hall of Fame. She earned a PhD in her seventies.