The four main areas of Connection in Human Design
HDS (copied from)
The obvious instant connection when you meet someone is when "sparks fly between you." This comes about when one person has one side of a channel and the other person has the other side. This is called an "electromagnetic" connection. When the two people meet, the energy combines to define the whole channel and the energies flow between the two centers. It can feel like a rush of energy in an otherwise quiet part of one's being. The more of these connections there are in a relationship, the more sparks fly. This can be very exciting, but too many of these connections bring a point when the relationship overheats!
When both partners in a relationship have the same gate or channel activation in their own design, the two combine in an area of friendship within the relationship. It is as though both parties are looking through the same window at the same view in their lives. Friendship leads to empathy and having several friendship connections potentially strengthens the harmony in relationships.
When one partner has an entire channel defined and the other partner has nothing in that channel, the partner with the definition has dominion in that area. This is a particular unique energy that your partner brings which you do not share in, but you may admire, appreciate or perhaps, simply tolerate. When you are the one who has the dominion channel in your design, it is helpful for you to be aware of the effect it has on your partner, i.e. you bring something to the relationship that your partner may be aware of, but in which they may not be able to participate
When one partner has a whole channel defined and therefore he or she is accustomed to consistently moving their energy in a particular way in that area of their being, but the partner only has a gate in that channel, there exists a state of compromise in the relationship. This area of the relationship bears much conscious attention. With compromises there can be potentially a mismatch of energy, leading to a sense of resentment because there is always the feeling that one or other of the partnership controls the flow in that part of the relationship.