International boundaries are places of abrupt transition, where a conceptual cartographic line can manifest itself physically in many ways. Along the US/Canada border, it is often in the form of a low fence or a cut-line through the trees, running along the path of the border. If roads head to the border in a perpendicular fashion, from either side, and do not hit a natural obstacle like a river, they are usually blocked by earthen berms, posts, guardrail, or overgrowth. If the road goes through the border, it usually has an inspection station, one for each country, on either side of the line.