Carcassonne: The Math
No, this is not some bizarre new variant. It is a discussion of one aspect of the tactics of play: the value of a tile. So often I see new players making odd choices. They fail to understand the simple math behind the tile placement. For the sake of clarity, I will be ignoring other aspects of strategy. This discussion is for the basic game only. Many of the expansions significantly affect the evaluation of scoring.
There are 72 tiles in the basic set. That means each player in a 2-player game will be placing 35 or 36 tiles over the course of the game. In my experience, final scores tend to be in the 100-150 point range. That's an average of 2.8 to 4.3 points per tile played. Do you need to score this much every time you play a tile? No, but there are considerations to maximize profit.
Roads would seem to be the least favorable play since each tile is only worth 1 point. Even so, new players love to take otherwise useless* road tiles and add them to one of their roads. This practice is often inferior.
In general, roads should be a secondary consideration. However, since roads appear on many tiles and must be connected as tiles are played, there often exists many 2/3/4+ unoccupied but connected road segments. If your meeple situation warrants AND the road(s) are reasonably situated, it is usually better to take advantage of an already created road than to extend one (1 point vs. 3+ points).
You can also get some sneaky points with roads. Consider the following case. You have a meeple at A on the south side of a 4-way intersection.
Adding the 4th tile and placing a meeple at B completes the road under A for 4 points and scores an additional 2 points for the new road.
These are perhaps the most misunderstood features for new players. Since they are worth 9 points, there is a huge incentive to play and complete them. However, each tile is still only worth 1 point for that cloister. Adding a tile to a cloister is the same as adding a tile to a road. Unless you need the meeple back, or there is some other reason, do not simply add a 1-point tile to a cloister.
The real value of a cloister is in its initial placement. 4 to 6 points is not uncommon. Also, placing a cloister against an opponent's feature means that your opponent will need to help you if they want to complete their own road/city. Also, 2 cloisters side by side allows for 4 of the tiles to be shared. This is still only 2 points per tile, but better than 1.
Always consider the value of a cloister as "in the bank". As yourself what you add specifically by playing the tile. Do not think of it as getting 9 points only when you complete it.
Cities are the most complicated of scoring issues. They can be worth 1, 2, or 4 points per tile depending on the size of the city and any shield icons present. Also, cities give points to farmers.
Unless you are trying to score farmer points, avoid making 2-point cities. Also, rather than starting a city for yourself each time, favor extending an existing unoccupied city cap with a non-cap piece.
If you have 2 or more incomplete cities, favor placing new city tiles onto the largest of them. This way you will more likely finish the larger cities, leaving the potentially incomplete smaller ones for the end game scoring.
If you have the option of extending a city or starting a new one by extending an unoccupied city tile, opt for the latter if you can spare the meeple. This is worth 4 points instead of 2.
Fields are very straight forward, but because their total value is accumulated until the end, they create an ever increasing tension as the game draws to an end. In addition, players incorrectly feel the need to attack opponents who have large fields.
Here's an example. Player A has a farmer (A) in a field with 5 cities (C):
This is worth 15 points (new farmer scoring). Player B wants to attack this field. To do so, he must play a tile/farmer, then later play another tile that connects the field. This means he must play 2 tiles AND take the risk that he'll even be ABLE to connect. Why not do this:
It's a single tile, it's no risk, and it still grabs all 15 points.
A related example. This time not all the cities are on the same border of the field:
Player A still has 15 points. Again Player B could attack this field with the same 2 tiles and risk. Player B could also play the same way as in the previous example:
Player B gets 9 points to A's 15. This is particularly good near the end game.
Cities + Fields
If you already have a field that you think you can keep control of, then the creation of cities changes quite a bit. Forming a 2 point city nets you 5 points overall. That's 2.5 points per tile. Using the "double cap" tiles to complete an existing city AND start a new one at the same time can earn you 10 points for 3 tiles.
Always ask yourself how many real points you are adding to your score, counting just the tile being played. This will help you evaluate your options when you add in all the other factors that occur in the game. If you find yourself simply adding to a feature you already control, you may want to think again.
* I would assert that almost no tile is useless. If you can't directly help yourself, you can either indirectly prepare for some future opportunity, or attack an opponent by trying to negate/steal/block a feature.