What is the author's style in The City of Ember by Jeanne DuPrau?

The story is written in the third person but from a limited perspective. The point of view alternates between Doon Harrow and Lina Mayfleet. The switching of perspective is barely noticeable to the reader but is necessary in order to keep the reader involved in the story line. An early example of this is seen when Lina and Doon are having their first days at work. Chapter two begins with Lina's first day at work and goes through her delivery of a message to the Mayor. While Lina is there, she finds her way to the roof of the building and captures the attention of the crowd below.