i'd start like Niek said introduce and define the topic and the economic activity. I'll use mine which is viticulture.
P1: Viticulture is ......[define]
P2: Comparison of past with present activity related to viticulture
P2: Where and why it occurs in these regions and why it related to present and past activities eg. in past grapes grew naturally in france and no due to globalisation wine grape seeds can be distributed around the world allowing for both new world and old world countries to grow wine.
P3: What the ecological factors are and what is the response to these such as the increased use of agrichemicals has lead to organic wines which uses less agrichemicals.
P4: sum everything up