Evidence Map: What You Can Check Yourself

The strongest educational resource is not a list of authorities. It is a map of observations that connect to each other. You do not have to personally repeat every experiment, but you should be able to see how each category can be checked. 
 At-Home and Low-Cost Checks 
 
 Shadow angles: compare stick shadows from two locations at the same time. 
 Polaris altitude: measure how Polaris changes height as you travel north or south. 
 Horizon distance: compare visible distance from different observer heights. 
 Moon orientation: track Moon tilt and phase from different locations. 
 Sunrise and sunset: compare times and directions across longitude and latitude. 
 
 Public Data Checks 
 
 Flight routes: compare great-circle routing with flat map expectations. 
 Weather satellites: compare visible cloud movement with ground weather reports. 
 Earthquake seismology: waves travel through and around Earth in patterns that reveal internal structure. 
 Surveying and geodesy: professional measurements account for curvature because large projects require it. 
 
 Why Multiple Lines Matter 
 Any single observation can be argued over. The power comes from convergence. Geometry, astronomy, navigation, physics, and engineering all point to the same shape without needing one central authority. 
 Suggested Confidence Ladder 
 
 Notice: the world looks locally flat. 
 Measure: small local tests reveal patterns. 
 Compare: different locations see different skies and Sun angles. 
 Integrate: the same spherical model predicts all of them together. 
 
 How to Use This Map in Practice 
 Pick one observation from each category: sky, shadows, horizon, navigation, and technology. You do not need all of them to be complicated. The point is to notice that they converge on the same model from different directions. 
 Beginner Path 
 
 Measure shadow direction and length at local solar noon. 
 Track the Moon for one week. 
 Check Polaris altitude if you are in the northern hemisphere. 
 Use the curvature calculator with a real shoreline target. 
 
 Advanced Path 
 
 Compare simultaneous observations with someone in another city. 
 Photograph star trails. 
 Compare great-circle flight routes against a flat map. 
 Follow public satellite passes and compare predicted timing with observation. 
 
 External Cross-Check Atlas 
 For a curated list of outside tools and public datasets, see Source & Tool Atlas . A strong learning path combines direct observation with independent prediction sources. 
 Distance Checks Against Flat Maps 
 Route distances are a powerful reality check because they are operational: airlines, ships, rescue planners, and travelers depend on them. Try the Flat Map Distance Problem page and its checker.