What landforms along the coast were important to both the british and the americans? why is shipping important to the economy of a place?

Those lands were important because it's where there's ports for the ships that would import and export goods are 

shipping is important to the economy because it's how you exchange goods and services with other nations 

Slavery was downright essential to mercantilism in eighteenth-century Great Britain. This was because mercantilism depended on the use of colonies to produce raw materials, particularly cash crops , for the mother country. These cash crops, with sugar being by far the most important, represented a major source of revenue for Great Britain.