Okay, so you know how maps show where different things are, like your house or your favorite park? But did you know that maps also have lines and numbers that help show how high or low things are compared to sea level? That's called elevation!
In Amsterdam, which is a city in the Netherlands, they have a special system called the Amsterdam Ordnance Datum (AOD) that helps them figure out elevation. It's kind of like a really big ruler that measures how high or low things are in the city.
The AOD is based on a point called the Amsterdam Zero, which is a certain spot in the city that has been chosen as the reference point for measuring elevation. It's like when you're playing a game and someone says "okay, from now on we're going to count from this point."
Using the Amsterdam Zero as a starting point, the AOD system helps people figure out how high or low different things are in the city. It's really helpful for things like building construction, making sure streets are even, and even predicting floods.
So, the Amsterdam Ordnance Datum is basically a system that helps people in Amsterdam figure out how high or low things are compared to a certain point in the city. It's like a big ruler that helps people build things and keep the city safe!