In the given question, a statement of Assertion is followed by a statement of Reason. Mark the correct answer.

Assertion: From the early years, the colonial government was keen on mapping.
Reason:  It felt that good maps were necessary to understand the landscape and know the topography. This knowledge would allow better control over the region. 

Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.

From the early years, the colonial government was keen on mapping. It felt that good maps were necessary to understand the landscape and know the topography. This knowledge would allow better control over the region. When towns began to grow, maps were prepared not only to plan the development of these towns but also to develop commerce and consolidate power.
The town maps give information regarding the location of the hills, rivers and vegetation, all important for planning structures for defence purposes. They also show the location of ghats, density and quality of houses and alignment of roads, used to gauge commercial possibilities and plan strategies of taxation.