(Pet peeve: mail#Etymology), not chain mail. While we are at that, the type of swords in fantasy that are called longswords should be called side-swords or arming swords, and bastard swords should be called longswords . Sorry for the nitpicking, it is not just about history but also about historical fencing practiced today.)
I primarily want to get an industrial revolution going.
I have worse than bachelor level knowledge of most sciences, but I definitely remember having learned in high school how steel is made today. And aluminium.
I think making a steam engine is not so difficult after you have the basic idea, Ancient Greece had it, just did not find it useful, having slaves. However steam ships that can sail without wind and probably eat less than 200 galley slaves would be interesting.
I remember the industrial revolution in Britain was started because a king wanted cannons made of cheap steel instead of expensive bronze so probably I need to work on the technique to refine steel quality, and I definitely remember we learned it in high school I just don't remember it myself much. But let's consider it part of the map. I think the basic idea is to heat iron with charcoal and use a lot of air blown in.
I would want gunpowder, I am highly suspicious whether going on conquests with modern arms would be at the end of the day as a total sum have positive or negative utilitarian consequences, but screw ethics: I just want to. I guess I would calm my conscience with forcing a Geneva convention type of thing on all countries and end painful methods of execution and things like that. At any rate, it is coal, sulfur and saltpetre, I just need to experiment with the ratio and once I have a basic idea of rifling it is probably not hard to implement so I can have far more accurate rifles than muskets and most importantly rifled cannons. On steam ships. Made of refined quality steel. Hm, this is starting to look good.
Also: https://www.topatoco.com/graphics/00000001/qw-cheatsheet.jpg
Imagine that you were instantly transported into (roughly) the 13th century. I'm not great at history, but I'm picturing sometime around the crusades. You're sitting there, reading this post on your computer, and BAM! Some guy in chain mail is asking you if thou art the spawn of a demon.
Given this situation, I present to you a challenge:
You are stranded in the past. You have no modern technology except your everyday clothes. The only thing you do have is your knowledge from the future.
What do you do?
I'll make this a little more structured for the sake of clarity.
1) You appear in Great Britain (or the appropriate analogue for your native culture).
2) Assume the language barrier is surmountable - in other words, it may not be easy, but you can communicate effectively (by learning the language, or simply adapting to an older version of your native tongue).
3) Further assume that you manage to gain the ear of a ruling lord (how is not important, just say you're a wizard or something) and that he provides you with enough money, labor, and expertise (carpenters, smiths, etc.) to build something *so long as you can describe it in enough detail*.
4) You are only allowed to pull from general, scientifically literate knowledge - high school/bachelor's level only.
5) You can't use your knowledge of future events to your advantage, as it requires too expert a grasp of history. Only your knowledge of the way the world actually works is available.
The reason for 4) has to do with the point of the question. I'm trying to figure out the kind of maps that we have today that are considered "general knowledge" - the kinds of things that are so obvious to us we tend to not realize that people in the past didn't know them.
I'll go first.
The germ theory of disease didn't achieve widespread acceptance until the 19th century. In other words, I'm the only person in the past who is quite confident about how diseases are spread. This means that I can offer practical advice about sanitation when dealing with injuries and plagues. I can make sure that people wash their hands before cutting other people up, and after dealing with corpses. I can make sure that cutting instruments are sanitized (they did have alcohol) before use. And so on. This should reduce the number of deaths from disease in the kingdom, and prove my worth to the king.
I'm trying to build a list of things like this - maps of the way the world really is that we take for granted.
Have fun!