Symbolism, Imagery, Allegory
Putting together a model of the entire town of Lakeview is a pretty daunting task—but not nearly as daunting as Mclean's task of letting her guard down and getting close to other people. The model town (and it's slow progress) is a symbol of Mclean's isolation and how she gradually begins to open up to other people and form roots in Lakeview. At the beginning of the book, there's only one little house on the table, all alone like our sad protagonist:
Together, we looked down at the tiny house, the sole thing on this vast, flat surface. Like the only person living on the moon. It could be either lonely or peaceful, depending on how you looked at it. (6.88)
Yup—they might as well be talking about Mclean. But with the help of some friends, our main girl starts to grow a community around herself and discovers that she likes being around other people and trusting them. As the model town grows and grows, so do Mclean's personal connections to the town of Lakeview. And in the end, when everything is finished, she sees that Dave and Deb have included touches that she didn't even consider—all the tiny model people:
"Other people, however," she continued, clearing her throat, "feel that by organizing the people, we are removing the life force from the entire endeavor. Instead, they think that we should just arrange the figures in a more random way, as that mirrors the way the world actually is, which is what the model is supposed to be all about." (16.143)
A model of the town and community isn't complete without people, just like Mclean's life isn't complete without all the people she's come to love. And when she notices that Dave has added figures representing memories he's made with her, well, we know for certain Mclean's not standing by herself anymore.