Cartographic aggression is when someone uses a map or a chart in a way that makes them seem more powerful or important than other people.
Think of it like playing a game and changing the rules in the middle of it so that you have all the advantages and nobody else can win. That's not fair, right? Similarly, when people use maps in a way that makes them or their country seem like they have more power or control over an area than they actually do, they are being unfairly aggressive towards the other people who also live in that area.
Sometimes, cartographic aggression involves physically changing the map, like when a country claims land that belongs to another country and redraws the borders on the map to make it look like the land belongs to them. Other times, it is more subtle, like when a map only shows certain information that makes one country look better than another.
Either way, cartographic aggression can cause a lot of problems and hurt feelings between people and countries. Just like it's not fair to cheat in a game, it's not fair to use maps to try and make yourself seem more important than others.