Back home (that hazy-barely-remembered-was-it-really-real? place that shouldn't be labeled in quite that way anymore, not when Narnia has been home for so long now in all the ways that really count), he colored and labeled maps in geography class, and each line, each letter of each name, seemed to him as though it had been established since the foundation of the world (they were mysterious, almost magical things, maps, beyond the reach of mortal men and full of the promise of adventure). If you'd asked him, he would have said that he knew (intellectually) because of history class that borders and town names shifted with wars and successions, but he had no real understanding of those changes, any more than he (Edmund Pevensie, an average, normal, everyday boy who may have dreamed of adventure, but never really believed he'd find it) understood any of the other daily duties of a monarch.
Now, here, where his life is full of talks of alliances and negotiations, avoiding wars and planning marriages, and any thoughtless word can cause an offense so grievous that it will end up affecting the lives of every person in both kingdoms, he knows that all cartography is politics (ironic that Narnia, which taught him what mystery and adventure were in all the ways that count, has robbed this one thing of its magic).