When you reach Renown 7, you will unlock a talent tree with various abilities. One of the abilities you can choose is called Cartographer Flag which says “Carry a flag with you to place on the highest peaks”.
There are locations scattered in the Dragon Isles in which you can place a flag on. Placing a flag rewards 250 reputation and there are 20 locations in total, which means 5000 reputation in total.

There is also an achievement: To place 10 flags called “Dragonscale Expedition: The Highest Peaks”.

Here are the locations of all highest peaks to place flags.
There are 5 flag locations in The Waking Shores. Check out the locations here. 
There are 5 flag locations in Oh´aran Plains. Check out the locations here. 
There are 5 flag locations in The Azure Span. Check out the locations here. 
There are 5 flag locations in Thaldraszus. 
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