Companion planting question
This is my first year in beginning my organic garden. I drawing out my plans for where I want to plant everything. I've purchased a book "Extreme Gardening" that focuses on gardening in the desert and has cross references the plants I should and shouldn't plant together. For the plants that shouldn't be planted together, what is a safe distance to plant them apart? For instance, it says not to plant Peas with members of the onion family, but a lot of the other plants and veggies recommend it. So, I am very confused on how to plan my garden. Any advice is greatly appreciated.