One of the questions faced in all forms of non-fiction writing is how much of the writer's own personality, experience, and viewpoint to include. Do you more or less leave yourself out, and allow the nature of your interest in a place to define who you are to the reader? Or, given that the work is also about you, is self-reflection a valid part of the literary journey?
A general answer to the problem may lie less with narrative voice than structure. A clear structure tells you how much of yourself to include.
Bill Bryson's Notes from a Small Island is structured around the author's final revisiting of the places in England that he's lived, before he and his family move back to America. The present journey is a farewell to England, and, as in the case of farewells in real life, it is natural to reminisce. His anecdotes, often gently ridiculing of both himself and the English, become the basis of a traveller's observations and analysis, and not the heavy-handed projection of himself onto the subject. Thus, although you are reading about Bryson for the entire book, you end his Notes thinking that you know more about the country than you do about him.
In William Dalrymple's The City of Djins, an extended stay in old Delhi is undertaken with an historian's sense of place, and the structure that the author adopts is to visit places in the city in roughly their historically chronological order. As part of this visiting of the past, Dalrymple tells us about the various problems and adventures of setting up and moving around in Delhi, and his landlady and his regular taxi driver become key characters. In the main, though, the historical quest is allowed to dominate: this is a story of a city's layers, and Dalrymple's function as a narrator is to unearth those layers for us.
The Snow Geese by William Fiennes is different again. His reason for travelling is actually to think about the nature of home, and so his growing homesickness during the journey is not a personal diversion but rather the delivery of a homecoming that the book has been meditating throughout. The structure of the work is a footsteps one, or, in this case, wing flaps. Fiennes is following the snow geese on their migration across North America and into the Arctic Circle. Their homecoming coincides naturally with his need for his own.
What these three examples have in common is an easy relationship between structure and personal content. And the lesson for travel writers, if we think of it in terms of craft, is to define your role as a character in terms of the task you've set yourself as a traveller. Are you, like Bryson, a humorous spectator; like Dalrymple, a chief investigator; or, like Fiennes, the philosopher with an eye for detail?
I'm sure there are other possibilities.
Bryson, Bill. Notes from a Small Island. Black Swan, 1996.
Dalrymple, William. City of Djins: A Year in Delhi. Flamingo, 1994.
Fiennes, William. The Snow Geese: A Story of Home. Picador, 2002.