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Force vectors are powerful aids that help you place parts on the PCB. When 
you place a part manually on the board, you should pay careful attention to 
the force vectors coming from that part. They allow you to place the part as 
close as possible to other parts that are attached to the same net.

Try to minimize the ratsnest distances from that part to other pads on the 
board. Force vectors work by treating the force vector lines coming from 
each part as if they were vectors, adding them together as a vector sum, and 
producing a resultant force vector. The resultant force vector has a length 
and direction. By moving the part in the direction of the force vector, and 
trying to minimize the force vector length, you are moving the part to a 
location that results in the shortest possible combination of ratsnest lines.

Force vectors are extremely valuable as a guide, but you should not follow them 

blindly. By the nature of the algorithm, all force vectors have a natural tendency to point 
toward the center of the board, because all ratsnests would have their shortest connections 
if all parts were located directly on top of each other in the very center of the board.

In Ultiboard, force vectors are represented by colored lines, although they 
can be dimmed. They appear by default, but can be controlled through the 
Information section of the Layers tab in the Design Toolbox. Refer to the 

 section of Chapter 3, 

, for more 

information about dimming and hiding force vectors. 

The figure below shows force vectors coming from parts.