user8637: I would like to improve my position evaluation skills. And as we all know - there are tons of tactical exercises , endgames studies, etc. But when it comes to exercises for positional evaluation - well - things are getting complicated.
So far I know these sources:
- 'How to Reassess Your Chess' workbook
- Aagard 'Positional Play' contains some exercises
- Khmelnicky 100-exercises test book (but it contains all kinds of puzzles)
I've read Dan Heisemann idea to work with complicated middlegame position and then process it with an engine. But IMHO it lacks clear plan presentation and overall view of what is going on the board. So my question is - can anyone point me to specialised book or webpage that contain more of position evaluation exercises with long descriptive answers? 

user12873: The sources you have (Reassess Your Chess and the Aagard book) are two of the best positional books out there.  I would definitely recommend getting those, if you haven't already.  The Reassess Your Chess book is better for really grasping the basics of positional play.  The Aagard book is more advanced, and it's better if you already have a solid positional base.
Another option is going to chess.com and getting a coach... there are many Grandmasters on there giving lessons at relatively cheap prices ($30 / $40 an hour).  You could maybe take 10 lessons and get them to just focus on positional exercises with you, which I think would be beneficial.  Some coaches on there are renowned for improving their students' play in an area very rapidly.  Although I think the two positional books I mentioned above should be good enough.

user-1: Three recommendations from me:

Mastering chess strategy by GM Hellsten has annotated games with more than 350 positional exercises with detailed answers. He has also authored Mastering opening strategy and Mastering endgame strategy
Chess strategy: move by move by IM Hunt isn't quite a puzzle book, but looks at annotated games and asks you questions as you analyse the games
Practical Chess Exercises by Ray Cheng has a mix of all types of positions (tactical and positional across all phases of the game). There are a total of 600 positions with detailed explanations here


8637: <p>I would like to improve my position evaluation skills. And as we all know - there are tons of tactical exercises , endgames studies, etc. But when it comes to exercises for positional evaluation - well - things are getting complicated.</p>

<p>So far I know these sources:
- 'How to Reassess Your Chess' workbook
- Aagard 'Positional Play' contains some exercises
- Khmelnicky 100-exercises test book (but it contains all kinds of puzzles)</p>

<p>I've read Dan Heisemann idea to work with complicated middlegame position and then process it with an engine. But IMHO it lacks clear plan presentation and overall view of what is going on the board. So my question is - can anyone point me to specialised book or webpage that contain more of position evaluation exercises with long descriptive answers? </p>
 12873: <p>The sources you have (Reassess Your Chess and the Aagard book) are two of the best positional books out there.  I would definitely recommend getting those, if you haven't already.  The Reassess Your Chess book is better for really grasping the basics of positional play.  The Aagard book is more advanced, and it's better if you already have a solid positional base.</p>

<p>Another option is going to chess.com and getting a coach... there are many Grandmasters on there giving lessons at relatively cheap prices ($30 / $40 an hour).  You could maybe take 10 lessons and get them to just focus on positional exercises with you, which I think would be beneficial.  Some coaches on there are renowned for improving their students' play in an area very rapidly.  Although I think the two positional books I mentioned above should be good enough.</p>
 -1: <p>Three recommendations from me:</p>

<ol>
<li><em>Mastering chess strategy</em> by GM Hellsten has annotated games with more than 350 positional exercises with detailed answers. He has also authored <em>Mastering opening strategy</em> and <em>Mastering endgame strategy</em></li>
<li><em>Chess strategy: move by move</em> by IM Hunt isn't quite a puzzle book, but looks at annotated games and asks you questions as you analyse the games</li>
<li><em>Practical Chess Exercises</em> by Ray Cheng has a mix of all types of positions (tactical and positional across all phases of the game). There are a total of 600 positions with detailed explanations here</li>
</ol>
