20-02-2001 21:20									#1
	Locating Foreign Cities Tired of ads?

Most players know that the unit location information on the city screen (unit "located near x") will give you a clue that you may be approaching a foreign city in unexplored territory. See the Free Information 1.1 in the CHEATS 3.0 thread. However, this same information and a little geometry can be used to find the EXACT location of the foreign city in question. This type of methodology can be very useful for finding SP trade partners when they won't trade maps, or locating opponents in MP games.

How It Works
Suppose you have a unit out exploring the world. Its initial location is "near Alexandria", your closest city. As you move away from Alexandria, the unit's location eventually changes to "near Babylon", a foreign city which is somewhere out in the black unexplored territory. Where is Babylon? The following diagram illustrates how to figure this out.

BBAAAA
EBBUAA__________A
BBBBAA_________/
BBBBBA________/
______\______/
_______\____/
________\__/
_________X
________/__\
_______/____\
______/
_____/
____/
___/
B

A = unit is closer to Alexandria
B = unit is closer to Babylon
U = unit location
A = Alexandria
B = Babylon
_ = other squares on the board

When you first notice that the unit's location is "near Babylon", move the unit a few squares left or right to find sets of squares to where the unit is closer to Alexandria (A) or Babylon (B). The boundary between these two sets of squares will be a straight line. Extend this straight line down your computer screen. (The straight line will not necessarily follow the horizontal and vertical grid of the screen. It may be something like "four squares to the right and one square down", much as if you were trying to locate the next goodie hut or a hidden special.) Next, draw a line from Alexandria to the closest point on the first line you drew. The point where the lines cross is labeled X in the above diagram. The two lines will always be perpendicular when they cross, a fact that cannot easily be illustrated in the above graphic. Count the number of squares from Alexandria to point X (e.g., "five left, four down"). Count the same number of squares from point X into unknown territory. The result, B is the location of Babylon. Note that Babylon will not necessarily be found in the direction of point E, the direction you were originally headed. Heading in that direction amounts to assuming that you were already on the straight line between the two cities, which is not necessarily the case.

Why It Works
The shortest distance between any two cities on the board is a straight line. The midpoint on this line (point X) is half way between the two cities. The set of all points which are equidistant between the two cities is a straight line through point X and perpendicular to the line between the two cities. When the exploring unit stumbles across this perpendicular line, the unit location switches from "near Alexandria" to "near Babylon". (The actual program apparently uses a simple algorithm to compute distance, but the effect is the same.) The above procedure does the geometry in reverse, working backwards from the current unit location to the location of the cities.

Accuracy
This method will locate the city within one square. An odd number of squares between Alexandria and point X, not having enough squares to get an accurate read on the line the unit is on, or cities or units which are very far away, will all decrease the accuracy of this algorithm.

Qualifications
This method will locate the closest foreign city, i.e., on the edge of foreign territory. Interior foreign cities cannot be located using this method, and this method will not work if there are other cities nearby.

edit: graphics

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[This message has been edited by Adam Smith (edited February 20, 2001).]

	20-02-2001 23:32									#2
	Support Apolyton buy from Amazon

hmm that is a lot of work. I always like to explore everything I possibly can. So i Just wait until I get within 2 squares and they b!tch at me to move. Although maybe that is 1 reason the ai never seems to like me

	21-02-2001 03:41									#3
	Support Apolyton, buy Civilization 2

I heard of that method before, just never saw it posted that much detailed. Generally, I'm giving thumbs up to that... but then, as stated before, it's very complicated, and I for myself will probably never use it. I do like the idea of it though

	21-02-2001 19:07									#4
	Remove this text

While this works very well against the dependable AI, in MP, it can sometimes not be effective. A few strategic city name changes can be used to lay traps for the exploring unit. When this method of locating was first being discovered. (have to credit Xin Yu with this one) he would change his closest city name to your closest city name on and off (depending on where your unit was) to make you think his city was 3 or 4 squares away from where it really was. It was always fun for your invading army to end up not where his city was, but in a carefully layed trap.

Or to be wandering thinking your unit was still closest to one of your cities only to stumble over one of his and quickly proceed to have the unit bribed or destroyed. When playing 2 on 2 games where I was his partner and trading maps frequently, I got to watch his expertise with these types of tricks. It was always very entertaining and instructional. I must admit that I don't use this trick very often because it requires a lot of effort and good recon. After a few beers you will make a mistake and the other player will notice something is amiss.

RAH

	21-02-2001 19:13									#5
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I sure hope they remove this "feature" from Civ 3. I think a good part of the fun in Civ is the exploration, and hate the free information you can get from this trick, clicking on black map squares, and using "where the heck is" to find unseen foreign cities.

	21-02-2001 19:31									#6
	Inflate your Upload Space

RAH:
I have heard of Xin Yu's renaming tactic. Fortunately there are few players as sharp as Xin Yu who can pull it off. Based on my limited experience (plus a PM to Ming) I had the impression that most MP players know the general location, not the exact location, of an opponent's cities. True?

	21-02-2001 19:51									#7
	Support Apolyton, buy Call to Power 2

AS
I suppose Rah is right (since he seems to have suffered from it) and Xin Yu has the credit (...once more).
Still, I never read about that method in the archive and I love it (just for the fun of it).
Thank you, AS.

	21-02-2001 19:53									#8
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Depends on your needs, but in general you are correct because that is the only need. But there are many times when you check it often enough that the location jumps out at you. This happens more often the closer you get. Within 8-10 squares you'll have a general idea where it is but when you get within 4-6 the exact location will become obvious. If you have three units out looking, you're usually better at finding the exact location. But again, knowing within a 4-6 square radius is usually good enough. One of the few times when I want to know exactly where it is, is when i'm planning a timed diplo tech steal to leapfrog a player to ace them out of a wonder. Then knowing exactly where it is, can be very beneficial.

RAH