One of my favorite ways to think about people is in terms of surface area. I find that it clicks in a satisfying, intuitive way for understanding people. This is a little abstract, so let's dive into some examples.
Reputation and Mindshare as Surface Area
One thing that has a fairly literal relationship to the idea of surface area is your reputation. Your reputation exists in the physical spaces that you inhabit, and the minds of the people that know you. Wherever people who are aware of you congregate is your "reputational surface area". As people forget about you, that surface area contracts and shrinks. As more people learn about you, it expands. Actors, for example, have massive reputational surface area, but it may be constrained by geography depending on where they're popular.
I generally find myself thinking about this idea in tandem with social viral phenomenon where your reputation tends to spread among people as they talk about you. Surface area is useful here because you can consider what places you're most likely to have a reputation that precedes you, where you're not, and where you might want to encourage its growth, all as actual physical locations. Physical locations are easy to think about, and make the problem of "what is my reputation like?" a little bit less abstract.
However, people only talk about you if you have a minimum "social activation energy", which basically means that people have to care about you enough (negatively or positively) for them to want to talk about you. This leads to "mindshare", a microscopic view of your reputation with an individual. If you love someone deeply, they have massive mindshare. You'll likely talk about them a lot, support them, and generally improve their reputation. In this case, the amount of surface area they occupy in your mind is very large. If you hate someone, you might also talk about them a lot, but perhaps to their detriment. Or you might want them to go away, and actively work to constrain or shrink their reputational surface area by refusing to talk about them or otherwise not encouraging other people to talk about them.
Social and Emotional Availability as Surface Area
Another area that I find surface area compelling in is when it comes to social interactions. Surface area makes it easier to understand why some situations are awkward or difficult and what makes people feel more open or closed off.
In downtown Austin, there are a lot of people who want to flag you down on the sidewalk--panhandlers, canvassers, and those people in the red shirts with the clipboards. Generally, strangers like to interact with people who seem open, accessible, and friendly. You could also say they like to interact with people who provide a lot of social surface area. There are lots of ways to reduce your social surface area in these scenarios: talking to a friend animatedly, talking to yourself, wearing sunglasses, using your phone, and more. I've noticed that I get interrupted less by doing something as simple as taking on or off a jacket as I walk by people who might want to stop me on the street. The important thing is that you're appearing busy, which makes people less likely to want to interrupt you. All of these fit pretty well into the idea of contracting the amount of surface area you provide for others to interact with you on.
If you wanted to go the opposite direction in expanding your social surface area, you just do things that make you seem more available. Don't wear sunglasses, make eye contact, walk slowly, smile, look lost.
Emotional availability (a willingness to become emotionally intimate with someone else - not necessarily sexually) is similar, but exists in the context of a conversation between people. People have different levels of emotional availability by default, and give a different amount to different people. Surface area as an idea is useful for noticing the "size" of someone's emotional availability. Do they bring up their childhood? How potent are their expressions of good and bad things that happen to them? Do they only talk about work? What topics make them go quiet? You can begin to "map out" someone's personality, preferences, and thoughts by paying close attention to how they act.
The more you do this, the more you can compare and contrast the people you know in terms of the "map" of their "emotional terrain". This makes it easier to get along with new people, and know who you want to talk to or avoid. This gets away from the pure idea of surface area, but you see where I'm going--transposing ordinarily abstract, emotional, or behavioral habits to a physical representation makes it easier to quantify those habits.
Surface area strikes me as intuitive because this is a world we live in with other people: a constant negotiation of space between us. If you have or have had a partner, you probably got to know them and their habits. How they talk, what they look like when they're sad, upset, jubilant, upbeat, conflicted, unsure. You know the terrain of their heart extremely well, and you know what it feels like when they shrink away, shuttered, or when they expand, flowering. It's less abstract. We can feel the difference. We play with our own surface area and give ourselves away in measured or unmeasured amounts, depending on who we're with and how we feel. I've found surface area to be an apt metaphor for most of these things; perhaps you'll get some usage out of it, too.