There is a "standard" way to consider normed spaces over arbitrary fields but these are not well-behaved in the case of scalars in finite fields. If you want to work with norms on vector spaces over fields in general, then you have to use the concept of valuation.
Valued field:
Let $K$ be a field with valuation $|\cdot|:K\to\mathbb{R}$. This is, for all $x,y\in K$, $|\cdot|$ satisfies:
- $|x|\geq0$,
- $|x|=0$ iff $x=0$,
- $|x+y|\leq|x|+|y|$,
- $|xy|=|x||y|$.
The set $|K|:=\{|x|:x\in K-\{0\}\}$ is a multiplicative subgroup of $(0,+\infty)$ called the value group of $|\cdot|$. The valuation is called trivial, discrete or dense accordingly as its value group is $\{1\}$, a discrete subset of $(0,+\infty)$ or a dense subset of $(0,+\infty)$. For example, the usual valuations in $\mathbb{R}$ and $\mathbb{C}$ are dense valuations. The valuation is said to be non-Archimedean when it satisfies the strong triangle inequality $|x+y|\leq\max\{|x|,|y|\}$ for all $x,y\in K$. In this case, $(K,|\cdot|)$ is called a non-Archimedean valued field and $|n1_K|\leq1$ for all $n\in\mathbb{Z}$. Common examples of non-Archimedean valuations are the $p$-adic valuations in $\mathbb{Q}$ or the valuations of a field that is not isomorphic to a subfield of $\mathbb{C}$.
Norm: Let $(K,|\cdot|)$ be a valued field and $X$ be a vector space over $(K,|\cdot|)$. A function $p:X\to \mathbb{R}$ is a norm iff for each $a,b\in X$ and each $k\in K$, it satisfies:
- $p(a)\geq0$ and $p(a)=0$ iff $a=0_X$,
- $p(ka)=|k|p(a)$,
- $p(a+b)\leq p(a)+p(b)$
In the case of a finite field, the valuation $|\cdot|$ must be the trivial one.
In fact, if there is nonzero scalar $x\in K$ such that $|x|\neq1$, then $\{|x^n|:n\in\mathbb{Z}\}=\{|x|^n:n\in\mathbb{Z}\}$ is an infinite subset of $K$, which is a contradiction.
Example of Normed space over a finite field: Let $K$ be any field with the trivial valuation (e.g. a finite field) and let $X$ be an
infinite-dimensional vector space with Hamel basis $B$. We can define
a norm $p$ by saying $p(e)$ is the number of nonzero coefficients
there are when we write $e$ as a linear combination of elements of
$B$.
But in this context, we have unexpected situations. For example, two
norms may induce the same topology without being equivalent. In fact,
consider the trivial norm $q$ on $X$ defined by $q(e)=1$ for all
nonzero $e\in X$. Then both norms, $p$ and $q$, induce the discrete
topology, but $p/q$ is unbounded. So there are no constant $C$ such
that $ p\leq Cq$.
A comprehensive starting point to read about normed spaces in this context is the book: Non-Archimedean Functional Analysis - [A.C.M. van Rooij] - Dekker New York (1978).
For more information on finite fields, I recommend the paper: Non-archimedean Banach spaces over trivially valued fields, Borrey, S., P-adic functional analysis, Editorial Universidad de Santiago, Chile, 17 - 31. (1994). There, the norm is assumed to satisfy the strong triangle inequality.
For the study of more advanced stuff, like locally convex spaces over valued fields I recommend the book: Locally Convex Spaces over non-Arquimedean Valued Fields - [C.Perez-Garcia,W.H.Schikhof] - Cambridge Studies in Advanced Mathematics (2010).
Best Answer
Since your question specifically mentions projective planes, let's suppose that we have the three-dimensional vector space $V = \Bbb F_q^3$ over $\Bbb F_q$, the finite field with $q$ elements (that is, $GF(q)$ in your notation).
One-dimensional subspaces
Let's start with the fact that a one-dimensional subspace $L$ has the form $L = \{c \mathbf{v} : c \in \Bbb F_q\}$; it consists of all scalar multiples of some vector $\mathbf{v} \in V$. In particular, there are as many points in $L$ as there are scalars in $\Bbb F_q$: there are $q$ of them, and $q - 1$ are nonzero.
But as you've pointed out, there aren't as many one-dimensional subspaces of $V$ as there are nonzero vectors in $V$ (when $V$ is finite, at least); two vectors $\mathbf{v}_1$ and $\mathbf{v}_2 $ determine the same subspace when they are scalar multiples of each other. Put another way, any of the $q - 1$ nonzero vectors in a one-dimensional subspace $L$ generate (in the sense of the "span of a set of vectors") $L$.
Thus, by counting nonzero vectors in $V$, we've overcounted one-dimensional subspaces by a factor of $q - 1$, so there are
$$\frac{q^3 - 1}{q - 1} = 1 + q + q^2$$
one dimensional subspaces of the three-dimensional vector space over $\Bbb F_q$. In your projective plane example, we have $q = 3$ for a total of $1 + 3 + 9 = 13\ \checkmark$ one-dimensional subspaces of $V$, or points in the projective plane.
Two-dimensional Subspaces
To think about lines in the picture, we need to understand two-dimensional subspaces of $\Bbb F_3^3$. Every pair of nonzero vectors $\mathbf{v}, \mathbf{w}$ where $\mathbf{v} \neq c \mathbf{w}$ determines a two-dimensional subspace of the form $P = \{c_1 \mathbf{v} + c_2 \mathbf{w} : c_1, c_2 \in \Bbb F_q\}$. This subspace contains $q^2$ vectors, and $q^2 - 1$ of them are nonzero. As we noted above, not all pairs of vectors in $P$ generate $P$: we must be careful that they do not lie on the same one-dimensional subspace. We can pick any nonzero vector in $P$ to start, and then any vector not in the span of the first; there are $(q^2 - 1)(q - 1)$ pairs $(\mathbf{v}, \mathbf{w})$ that span $P$.
To count two-dimensional subspaces, we pick two nonzero vectors in $V$ not lying in the same one-dimensional subspace, and then take care of overcounting that arises due to multiple ways to generate the same plane: there are
$$\frac{(q^3 - 1)(q^3 - q)}{(q^2 - 1)(q^2 - q)} = 1 + q + q^2$$
two-dimensional subspaces of three-dimensional $V$, the same number of one-dimensional subspaces! Food for thought: wouldn't it be nice if there was a "natural" bijection between the one- and two-dimensional subspaces, in our three-dimensional space?
Specific one-dimensional subspaces
To list the points of this projective plane, we can list $13$ vectors in $\Bbb F_3^3$ that don't lie (pairwise) in the same one-dimensional subspace:
\begin{array}{lll} (c, 0, 0), & (0, c, 0), & (0, 0, c) \\ (0, c, c), & (c, 0, c), & (c, c, 0) \\ (0, 2c, c), & (2c, 0, c), & (2c, c, 0) \\ (c, c, 2c), & (c, 2c, c), & (c, c, 2c) \\ & (c, c, c), & \\ \end{array}
where here $(2c, c, c)$ means $\{c(2, 1, 1) : c \in \Bbb F_3\}$.
To get some experience with vector spaces over finite fields, you should actually write out elements in some of these subspaces, and convince yourself that all $26$ nonzero vectors of $\Bbb F_3^3$ live in exactly one of these one-dimensional subspaces.
Specific two-dimensional subspaces
These are messier. It's easy to pick two linearly independent vectors $\mathbf{v}, \mathbf{w}$ and write some subspaces $\operatorname{Span}(\{\mathbf{v}, \mathbf{w}\})$, but listing them all, and without repeats, is a bit tedious (and not exactly easy!).
Instead, recall that two-dimensional subspaces can always be described as the solution set to a linear equation $\{(x, y, z) : ax + by + cz = 0\}$ (just like you're used to with vector spaces over $\Bbb R$), and each such equation is "uniquely" determined by a vector $(a, b, c)$ normal to the subspace. This is great, because we just computed all the one-dimensional subspaces! With a bit of work, we can write down what generic elements in our two-dimensional subspaces look like:
\begin{array}{lll} (0, a, b), & (a, 0, b), & (a, b, 0) \\ (b, a, 2a), & (a, b, 2a), & (a, 2a, b) \\ (b, a, a), & (a, b, a), & (a, a, b) \\ (a, b, a + b), & (a, a+b, b), & (a+b, a, b) \\ & (a, b, 2a + 2b), & \\ \end{array}
where, for instance, $(a, b, a)$ represents the subspace $\{a(1, 0, 1) + b(0, 1, 0) : a, b \in \Bbb F_3\}$. Additionally, it's in the same place as $(2c, 0, c)$ in the previous table. This signifies that the subspaces are orthogonal: $(2c, 0, c) \cdot (a, b, a) = 2ac + ac = 3ac \equiv 0 \pmod 3$.
Again to build familiarity, it would be good to pick a subspace or two and write out all vectors in these subspaces, as well as the one-dimensional subspaces it contains.
The good news here is that projective planes have lots of symmetry (in fact, yours has 5616 automorphisms!); you can start building a correspondence between vectors and points in the image freely, although before long, you will have to be careful about how you're constructing things (to make sure points on the same line correspond to one-dimensional subspaces in a common two-dimensional subspace). It's probably better to create the image from scratch, using the picture as a guide for what should happen.
A note of caution
I didn't write out things for a general $n$-dimensional vector space, because things get more complicated. Another source of difficulty is the structure of $GF(p^n)$ for prime $p$ and $n > 1$. When you're working over $GF(p)$ for prime $p$, things are nice: You're just working in the ring $\Bbb Z /p\Bbb Z$, doing arithmetic modulo $p$. But this stops being the case in $GF(p^n)$, and I personally don't know how to work "quickly" in such a field, which is often constructed as a quotient of the polynomial ring $GF(p)[X]$ by an irreducible polynomial of degree $n$.
Hopefully you've played around with the Fano plane too, things are very nice there!