Shadow Lines uses the symbolism of maps and in particular borders throughout its novel to identify and explore a key postcolonial theme. Postcolonial criticism examines and criticises man-made boundaries and borders as attempts to define a particular group as against another group ("the other"). Postcolonial criticism attempts to rupture these apparently secure boundaries by examining those who live on the margins of these boundaries and also deconstructing (taking apart) the notion of the other. This is particularly true of the "invention" of India the nation, with the Partition of 1947 which drew imaginary lines across India, creating the countries of Pakistan, Bangladesh and India and also causing much death from the resulting riots.
The narrative in Shadow Lines is constantly transgressing boundaries of space and time, thus giving the novel its title, as the lines that divide places and even times are shown to be easily transgressed - "Shadow Lines." Borders are thus shown to be "illusory" and "shadowy" and often "born out of different strands of nationalism and ideology" that in turn give birth to violence. In this novel as in life there are multiple boundaries and dividing lines, not just national boundaries, but borders that separate the coloniser from the colonised, the "us" from the "them", and borders also in time, separating the past from the present. These borders are ever changing as the perspective from which we look at them changes.
Consider this quote regarding the inherent fragility of boundaries:
[About seeing the border from the air] But if there aren't any trenches or anything, how are people to know? I mean, where's the difference then? And if there's no difference both sides will be the same; it'll be just like it used to be before, when we used to catch a train in Dhaka and get off in Calcutta the next day . . . (151)