Embolism: Understanding Causes & Locations (Arteries, Veins, Heart)

Question
why does embolism only happens in the arteries and why pulmonary embolism is usually due to a clot from the legs. Why is cerebral embolism is usually due to a clot from the heart.

Answer
clots come from the veins and the heart atria in which blood moves slow and is started due to high plant oil diets see http://efaeducation.nih.gov for a FREE software program to identify the foods causing the excess plant oil in the diet that leads to increased clotting
The location is simply downstream from where the clot begins