How do television announcers read putts?

Just guessing, but I'm sure they have the same detailed maps as the caddies - plus, most of the "movement" comments come from the on-course reporter who is down there.

Some of it you can see from the TV, some of the commentators have played the courses, and a lot of it comes from going out in the morning to read the greens.

I think they mostly have notes about the greens from prior rounds played by golfers or have seen what the putts have done from the golfers that have already been through the hole that day.

Yup

Perhaps some sort of mapping and contour device is used months prior which then creates from a clay mold a miniature green, say 3ft x 3ft,  precisely as found on the course. Then the TV  guys just pull out the 3rd green from the rack  of 18 and mark the position of the ball.  The clay mold never changes unless the green itself is modified. 

Some of the time it's because they happen to be in the tower above the green, sometimes it's because they have notes, sometimes its because they've seen others try that putt earlier, and sometimes its fed to them through their earpiece from someone they have at the green. It by no means is always a correct read that they will give you, contrary to what they lead you to believe.

Also, it's easy for Johnny Miller to read greens from the 18th tower as long as he has a compass, since all putts break towards Lake Merced.

Some of the tournament courses have computer simulations of their greens that show which way the breaks run. Combine that with seeing the early groups play the hole, and this gives the announcers details for that day's cup.

All of the above and even with that, they are not always right.  Roger Maltbie was saying that Tiger`s putt on 15 looked straight with only a hint of right possible and it looked like he started it outside left and missed a cup or more on the right...Dufner had the same putt and also had it dive right. 

 

Any read can vary with the speed at which the putt is hit.  Some players play the ball well past the hole, others try to die it into the hole, and that can change the break drastically on a big breaking putt.  If the putt isn't hit at the speed that the announcer's information was taken at, then the line will be different.

Exactly. When I take a playing lesson from my usual teacher, I always have to add an inch or more of break because I prefer the ball to turn into the hole on its last revolution, where he likes it to go a little bit past the hole.

Because they've been watching players putt on the green all day long from same positions.  

Pretty much that.................

I have a friend who was a "spotter" for the US open.  They relay up to the guys announcing anything from the break of the putt, to the lie of the ball (in rough/sand), to the branches in the way of a shot...  I'm sure the announcers have a pretty good idea of the break of the putt, but they also get information this way.  Not to mention how they often "send it down to Dotty," or "Send it down to Rog."
 

I have worked quite a few tournaments. I have seen Johnny Miller driver out to the last 2-3 holes early on before the players get there and hit many (30?) putts from various angles and lengths so that he has a feel for those holes. Like him or hate him, he does appear to do his own homework.