The coordinate plane
One number says where a point sits on a line. How do you say where a point sits on a flat sheet?
Where you are 4 inside
What this area is about
Cross two number lines at right angles, meeting at the 0 of each, and every point of the flat plane gets a pair of numbers (x, y): how far across, then how far up. Once points have numbers, a picture can be described in numbers, and a list of number pairs can be drawn as a picture.
How these fit together
The definition. Ordered pairs and the first quadrant sets up the axes, the origin and the pair (x, y), using only numbers that are positive or 0, and shows why the order of the two numbers matters.
Extending it. Plotting in all four quadrants lets either number be negative, so the pairs reach every side of the origin.
A result. Reflections across the axes shows that changing the sign of one coordinate mirrors a point across an axis, and changing both turns it a half turn about the origin.
A use. Two patterns and their graph pairs the matching terms of two number patterns and plots the pairs to see how the patterns relate.
A path through it
Start with ordered pairs. Two patterns and their graph needs only the first quadrant, so it can come any time after. Plotting in all four quadrants comes before reflections across the axes.
Finish here and you can read and plot any point. The distance formula, graphing a line from a table, scatter plots and reflections all build on it.