How it works
How the points and the 3 versions are made
Every point on a worksheet is a grid point you placed, written in the numbers of its version. Here are the rules in the order they run, a worked example you can check, and what the maker does not do.
Last updated 19 October 2026. Written by the Plotpicture team.
The rules, in the order they run
- The drawing grid. You draw on a grid of 5 to 40 squares each way, with the origin at the bottom left and y going up. A point can never sit outside it: a tap or a pen line outside the grid adds nothing, and the page says so.
- Snapping. Every point goes to the nearest grid point. By default that is a whole square; you can choose half squares, quarter squares or tenths. A position exactly halfway goes up and to the right.
- Simplifying pen lines. The pen keeps every grid point it crosses. Then the first and last points are kept, and between them the point furthest from the straight line joining them is kept if it is further than the tolerance you set; the same test repeats on each side. Points exactly on a straight run are always dropped. Only points you drew are ever kept, so every point stays on the grid. The line and shape tools keep each point where you put it.
- Shapes and Lift pen. A shape is one line the student draws without lifting the pen. Only Lift pen (or closing a shape) ends it: changing tool keeps the pen down, so a shape can mix straight edges and pen curves, and undo keeps it open. A pen line that starts where the open shape ends carries on; one that starts anywhere else begins a new shape. A closed shape lists its first point again at the end. A point that repeats the one before it is left out of the list, and a shape with only 1 point is left out of the worksheet, each with a note.
- Counts. A worksheet needs at least 2 shapes or 10 points, every shape needs at least 2 points, and a worksheet holds at most 400. Past 150 the page warns that the lesson may run long.
- Version A, integers in the first quadrant. The picture exactly as drawn. The drawing grid is the first quadrant, and each square is worth the scale you choose: 1, 2, 5 or 10.
- Version B, integers in four quadrants. The middle of the box around the points the student plots is found, rounded to a whole square (of the two nearest, the one that needs the smaller grid, then the nearer), and the picture moves by that many whole squares so it sits across the axes. The grid reaches at least half the drawing grid each side of the origin. Squares are worth the same scale as version A.
- Version C, decimals or fractions. Each square is worth 0.5, 0.25, a half, a quarter or an eighth, in the first quadrant or across the axes. This is the scale rule: when your drawing uses parts of a square, each square of your drawing can become 2, 4, 5, 8 or 10 squares on the sheet. The engine picks the smallest that puts every point on a grid line while the sheet stays within 40 squares a side, and the page says which it chose.
- Flagged, never rounded. A point that would fall between grid lines in a version is named by its number and ringed on the grid, and that version cannot be downloaded until it is moved. Choose the shape and the point to move it one snap step at a time, snap it to a whole square or delete it; Snap every point to whole squares moves them all, only when you ask, and says how many moved. A flagged point is never written on a sheet as a value.
- The sheets. The point list runs in columns, numbered in plotting order, with Lift pen between shapes. A printed square is never under 3 mm or over about 1 cm. Labels go every 1, 2, 4, 5 or 10 lines; if they would overlap at that size the page refuses and names a spacing that fits. Grid lines are vector lines in the PDF. All numbers are exact: a coordinate is a whole number of squares times the value of one square.
Worked example: the kite starter
The kite is drawn on a 20 by 26 grid, in 7 shapes and 28 points. With the squares worth 1 in versions A and B and 0.25 in version C:
- Version A: Integers in the first quadrant: the picture as drawn, x from 0 to 20 and y from 0 to 26. Each square is 1.
- Version B: Integers in all four quadrants: the picture is moved 10 squares left and 13 squares down so it sits across the axes, x from −10 to 10 and y from −13 to 13. Each square is 1.
- Version C: Decimals in the first quadrant, x from 0 to 5 and y from 0 to 6.5. Each square is 0.25.
The first shape, point by point. Check any row: B is A moved, C is A times 0.25.
| Point | Version A | Version B | Version C |
|---|---|---|---|
| 1 | (10, 24) | (0, 11) | (2.5, 6) |
| 2 | (15, 19) | (5, 6) | (3.75, 4.75) |
| 3 | (10, 10) | (0, −3) | (2.5, 2.5) |
| 4 | (5, 19) | (−5, 6) | (1.25, 4.75) |
| 5 | (10, 24) | (0, 11) | (2.5, 6) |
What it is not
- It does not trace an image for you. A loaded image is a faint guide under the grid; you draw over it, and it never prints.
- It does not round. If a point does not fit a version, it says so and waits.
- It does not reorder your shapes. The plotting order is the order you drew, unless you move a shape.
- It is not a marketplace and has no licensed characters. The 24 starter pictures were drawn for this site.
- It does not send anything anywhere. Drawings and images stay in your browser.
Try it on the mystery picture maker, open a starter picture, or read the guides for the lesson.