The 'Humble' fields are one of the most essential and enduring Districts in Brunelleschi. Don't let the fact that you start out with one for free cause you to underestimate the importance of the Field's products and Bonus Buildings. Let's take a look at what makes this District unique and how you can turn it to an early advantage.
Main Building - The Granary!
The Granary Exterior in Oculus View
Granary Interior Oculus View
Minister of Agriculture Desk
Exclusive Building - The Latifundia!
You won't find a less expensive way to house NPC 'Peers' than the Latifundia, a palatial form of housing that allows your 'noble' residents to support themselves via farming. The Peers won't pay taxes on this income directly, but they will work in your other buildings and the overall increase to Agricultural Efficiency is noteworthy! You'll quickly find a balance of Latifundia and Farms that produces the huge amounts of grain, hemp, and produce to expand quickly and start other Industries.
Linked Building - The Farm
Farms are the basis of your early Economy and can be established almost gratis. It takes ~2 minutes to construct a L1 Farm so they make the perfect building for 'using up' idle workforce and solving unemployment. Farm Products are the basis of many Light and Medium Industries (Grocers, Weavers, Alchemists, Brewers, Bakers), and essential to the Transportation Industry as well. Farms produce a higher volume of Food products on the whole than other sources (except perhaps fishing) so it can serve as a great way to keep your population fed and happy.
The Linking Bonus of the Farm when built in the Fields makes these the most efficient possible farms. A 10% bonus to output becomes notable quickly (A L10 Farm in the Fields is as powerful as a L11 Farm elsewhere).
Minister - The Minister of Agriculture
While not a figure to strike terror into the hearts of opponents, a talented Minister of Agriculture can really make a difference in a settlement's growth and economy. Being a Rank 1 Ministry it's ideally suited for starting Lords who want to gain Importance and learn the ropes of District Management. In Larger/Older Settlements it can still serve as an excellent (and Significant) position for training new members of Government.
Downside - Low Rank District
The Fields will always have the problem of being an R1 district. This will limit the Garrison Space and Defense Rating of the District and leave it fundamentally open to attack. With only 27 Building Plots to start (and 35 Fully Upgraded) it won't be the biggest or richest district for long in any Settlement, and with only 4 Attributes providing bonuses from the Minister, no up-and-coming young Lord will want to be trapped behind that desk for very long. Ultimately the Fields will suffer from a somewhat single-focus nature. Fluctuations in the Hemp/Grain/Flax/Herb/Produce market will hit this District the hardest.