What does development actually...DO?

[Hans_Lemurson 1]

I can't figure out what investing in the development of a province actually accomplishes.  It has no noticeable effect on Tax income, nor on Production income.  You can invest thousands of gold into a province but not, as far as I can tell, actually gain anything from it except a slight increase in Administrative costs.

Is there some important game mechanic I'm missing here?  What does the "Development" level of a province do?

Edited January 1, 2019 by Hans_Lemurson

[SLiCK_Mx 23]

Development level determines the effectiveness of your economy. I'm pretty sure it's a modifier in calculating the income you get from a province. So it's best to make sure that your provinces are well developed. Also it affects your rank scores.

[Hans_Lemurson 1]

I have conducted some research on this, using Korea (with no tech points applied) as a test nation and I have found at least two things that Development does: 

• Development will act as a multiplier on your Production.  Still working out the numbers.  Spending 7000g raising development from 0.235 to 0.344 boosted my Production from 222 to 268.  Admin costs also rose from 378 to 388, so the net income boost was just +36g/turn.  In 200 turns that investment will finally pay off.
• Development reduces the cost of Economy.  Raising the Dev from 0.235 to 0.344 lowered the price from 8.95/unit to 8.70/unit, which will save you 250g for every 1,000 economy you build.  It's not a lot, but it's better than nothing.

People advocating economic development by and large seem not to have run the numbers.  And just about every economic investment scheme I've tested has a Period of Return of about ~150 turns.  That seems rather...low.  Maybe there's some hidden synergies somewhere?  I'll look into Research next.

Edited December 30, 2018 by Hans_Lemurson

[Cai 17]

Development is actually cheap late game, compared to its benefits, it increases the rate at which your province grows. 

For early game, you should only increase development on your most valuable provinces, while ignoring your weakest ones. [As a recommendation, just increase development for provinces above 5000 Economy and is below 0.30 of your tech level] 
Example:

A 9000 economy with 0.35 development on a 0.40 civ should basically be ignored

A 9000 economy with 0.35 development on a 0.85 civ should be upgraded

An economy that takes up 1% or above of your economy when you have over 100 provinces or 5% and above for 20 provinces should be prioritized.

[Hans_Lemurson 1]

AoC2 seems to be a game where making an investment that takes 150 turns to pay back is considered "Fast".

I've continued to experiment with the economy, and I've found something important:

• When you use the "Investment" slider in the Budget screen, it adds Development to all your provinces.
• The amount of development added is based solely on the "Province Growth" rating of the province, and what Percentage of your budget is going to "Investment".
• Development growth rate maxes out at +0.00531 for any "Province Growth" higher than 80%
• The quantity of money spent has no effect.  Feel free to drop taxes to a minimum while doing this.
• Speed of development seems unaffected by technology.

Building Development via the Budget is significantly cheaper (in terms of total Dev built) than doing province-based "Invest in Development", but the cost is that your gains are spread across the entire empire regardless of efficiency, and it's not fast.  Going from 0.3 Dev to 0.5 Dev would take ~40 turns even in your best provinces.

Of course "Investment" also builds Economy in your provinces at the same time, but the Economy gain is only half what it would be had you spent the money directly in a province.  But given that you're also getting a bunch of Development built everywhere, I think you can view it as "Half your Investment money builds Development, half goes to Economy".