Sir Cumference and the Viking's Map

For fans of the Sir Cumference series with coordinate geometry on their mind, here is the seventh installment in this fun look at math and language.

While riding through the forests of Angleland, cousins Per and Radius realize they are lost and are desperate for a map to guide them home. Soon they come across a mysterious house in the hills. Inside they find a map to a treasure belonging to Xaxon Yellowbearyd, the fiercest Viking warrior of his time. Per and Radius must decode the strange numbered grid on the map, while trying to steer clear of the pack of bungling bandits who are on their tail. Will they find the treasure in time?