Secret Water — Arthur Ransome

In the eighth book in Arthur Ransome's beloved Swallows and Amazons series, the five Walker children are left on a "desert island" by their parents with provisions for a long stay and a blank map to fill in. Like all of Ransome's books, this is at once a real adventure and a lesson in the practicalities of exploring - in this case, of surveying the inlets, coves, mudflats, and estuaries of "Walker Island." Naturally, there are enemies to overcome (another clan named "The Eels") and friends to meet (who else but the intrepid "Amazons?"). And, as always, the children do it all solo.