We have expanded the preceding port railway to the top and bottom. Once again, bottom yards interface with main freight railways. Those switches whose spurs extend off the layout area on the bottom are connected to a mainline railroad. The spurs in the upper left can service local industries or connect with a larger railroad. Industries would include nautical parts manufacturers and services, such as the propeller works, anchor and chain makers, etc. A major product coming through a port like this is fuel for ships, either oil for modern ships or coal for earlier ones. Be aware that such coal refueling is itself a major operation.
Here we expand to the lower right, with a 4' by 7' extension representing an inland railroad. Spurs serve various industries. A coaling industry or fuel refinery would be very appropriate for providing fuel for ships, and ought to be one of the major industries serviced in the extension.
Another extension, this time to the lower left. It is full of spurs and sidings to service manufacturing industries who would ship products and receive materials from overseas.