We started out our "Character Analysis" of Davie by saying that everything that happens in Kidnapped is focused through him. Well, that's as true of characterization as it is of plot developments. As the narrator, Davie influences our perception of every character in the novel – especially of Davie himself. An example of such characterization would be this line about Alan: "For though [Alan] had a great taste for courage in other men, yet he admired it most in Alan Breck" (12.55). Davie is coming out directly to tell us that Alan is vain and boastful about his courage.
Take a gander at our "Symbols, Imagery, Allegory" section and you'll see that all of the symbols we found in this novel are dedicated to identification: Alan's French clothes show that he's a Jacobite, while the hidden or half-hidden Highland tartans of the men Davie meets demonstrate which clan they belong to. What's more, Davie and Alan's wanted posters both describe the two of them more based on the clothes they're wearing than anything else (which, in Alan's case, is a good idea, since he refuses to change his clothes). In Kidnapped, clothes show the politics, the family, and the social class of the wearer.
As we keep saying, in Kidnapped, it makes a huge difference whether you're from the Scottish Lowlands or the Highlands. The Lowlands are both physically and culturally closer to England (although they have their own resistance movement to English imperialism, the Covenanters). This means Protestantism, Scots language, and, in some cases, pro-English-monarchy. The Highlands, on the other hand, have a visibly different culture. Most of the residents speak Gaelic, many support the Stuart family's claim to the English and Scottish throne, and all belong to clans with a confusing number of allies and rivals. Location goes a long way to determining politics, religion, language, and even clothing in this novel.