In case I die before I finish these, here are overarching plans for large scale land development for Westeros. Use these plans to bring prosperity to our kingdom.
The Neck.
The neck is a massive problem for the nation, given it essentially cuts off the north from the rest of the kingdom, except through a narrow, useless road.
The solution is simply to drain it. All of it. Make the crannogmen into farmers, and make use of the land for farming. The soil should be rather good. More importantly, destroying the north's ability to defend itself from southern invasions is paramount to keeping the province In line.
The Stepstones.
Finish the dikes around it. The point of these dikes is to turn the Stepstones into what is essentially one giant freshwater lagoon, with a massive number of internal islands surrounded by what will eventually be canals between the internal islands.
You must also make certain to upkeep canals in and out of the lagoon, given how incredibly important these will be for trade.
The dikes must be immensely powerful, strong, and thick, given they will have to stand up to the storms that swoops in from the summer islands to hit the Stormlands. Follow durrans example, and if the first don't work, try, try, and try again until they stand.
Would be nice to recreate the land bridge between Westeros and essos completely, with only a few westerosi controlled canals to allow ships to pass through, thus enforcing complete dominance over trade and making smuggling much harder.
This would only be achievable if one controls both the disputed lands, and Dorne however. So it will be kept a large island/archipelago.
The land must never be granted to dukes or counts, only viscounts and barons. Keep full Control over it. It will be the most fertile piece of farmland on this planet, and unlike the farmland in Blackwater Bay, it will never have to suffer winter. It will be an incredible money maker, even without controlling the trade that passes through.
Making Dorne bloom.
I have absolutely no interest in incorporating Dorne into my realm, and personally I prefer to make sure our relationship will only be about trade from now on.
That said, if any of my successors annexes the nation, here is how to make Dorne bloom.
The reasons for the dry desserts of Dorne existing is the red mountains. They make sure that the common rains from the sunset sea never passes front he reach into the mountain.
The process through which this happens is very complicated, and I cannot easily explain it here, but basically, all you need to know is this.
Rain originates from water evaporation under the sun, and in the case of Dorne, those same mountains that keeps the evaporated water on the north side of the mountains, will similarly do the same with any water in Dorne. If one were to introduce massive water evaporation in Dorne, the subsequent rain will stay in the region.
Thankfully, there is a method for doing this.
Namely, the torrentine, the enormous and powerful western River.
All one needs to do, is create a massive waterway through the lands to the east of the mouth of the river, through the mountains, then make a waterway to the lowest point in the red dessert, then finally, redirect the water into this dug out canal, and watch as a massive fresh water lake forms in the desserts of Dorne.
This however, is only step 1.
The next step is to take into consideration what will happen next.
Firstly, you must make certain that the lake has a drainage river into the sea. Whether naturally formed, or just a dug out canal doesn't matter, the water must flow. If it does not, this massive lake will become a saltwater one. That is not desirable.
Eventually, if the lake has a drainage, the salt in the sand will dissappear, turning it into a full freshwater lake. The river will also become a freshwater one, and frankly, it will probably be the site an incredibly fertile riverbed.
The longer it is, the better.
Secondly, there is the rain. Introducing such an enormous amount of water into the dessert will cause massive amounts of rain falls as massive amounts of water will evaporate.
This in turn will create countless smaller oasises, and if you're really luck, smaller lakes that can be connected to the large one.
The rain will also help Dorne's already existing rivers, as well as the new one, as massive amounts of rain will just make them bigger.
The eventual goal of this entire effort will be to turn all of Dorne into a massive savanna, essentially creating an environment similar to that which can be found around it's rivers, now across the entire nation.
Utilize the same methods the dornish use to make land by the rivers more fertile by planting shade, only on a much larger scale.
Canals.
I have already laid the planned foundations for two canals through Westeros, but I will most likely not live to see more than these two to completion.
Thusly, I will leave a list of the canals you MUST make, if I don't live long enough to see them happen.
The northern canal, and the Ironborn Bay-Blue fork canal have already been planned out, so I'll not go into them here.
Instead here are the rest.
Gods eye-Trident canal. Where it ends on the trident part doesn't matter, so long as it's fresh water on both sides, that way you don't need to worry about salt contamination, and don't need to bother with complicated water locks.
Green Fork-Bite Canal. A canal connecting the bite to the trident, making travel much, much quicker between the north and the Riverlands. Will need a water lock on the Northern part.
Blackwater-Meander Canal. A canal Connecting the Reach to the capital. Make certain that the crown maintains all control over this canal.
Last river-Long Lake canal. A less important one in the north to allow travel easier between the lake and the long river to the west.
White Knife-Torrhen's Lake. Another smaller canal, connecting the lake to the great waterway of the north. Surprisingly important for torrhen's squares development given that travel down the river Saltspear is impossible for boats given the massive amounts of waterfalls.