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Bigger brains in North America I would suppose.
Pic rel is a survey disk. You can do some research and find where your is in your town. These are benchmarks that all surveying is built from. When you are building a project from a bridge, skyscraper and right down to a home, you can request the local survey. Each survey builds off the other, with known points. That disk is indicating an elevation above mean sea level (mid point or high and low tides).
Now think of the concept of sea level on a round earth. Every direction you want from this benchmark you are going downhill away from that point. If you walk a mile there is a new sea level 8" lower.
Go to your city and request local sanitary and storm sewer lines. They are all hidden underground, so we need accurate drawings of where they are found. You put in a new house, dig up your front lawn and connect into the City sewer lines. There is no curve to these lines and the run under every city. Sewer lines are a gravity drain that slopes to the treatment plants. They are all about 15' below street level. Imagine the earth being round and you having to slope from your house to a City treatment 80 miles away. The line would be deeper than the grand canyon. And, no house along the way would be able to connect.
It is flat as a pancake my friends. It is the only way it can be.
