Dotted Grid

By the end of this lab you'll be able to:

• Place dots at every intersection of a grid using nested loops
• Use dot() to draw a filled circle in one line
• Map a loop variable to a visual property (dot size) to add depth

One hundred steel-blue dots fill a 10×10 grid. Each row of dots grows a little larger, so the bottom looks heavier and closer — a simple trick for creating depth.

Welcome to the Dotted Grid!

In this lab you'll discover dot() — turtle's one-line circle command — and see how mapping a loop variable to size adds a sense of perspective to a grid. Let's code it together!

How the Grid Works

Two nested loops step through every (row, col) pair from (0,0) to (9,9). The position of each dot is:

• x = -180 + col * 40 — 10 columns, 40 pixels apart, centered on the canvas
• y = 180 - row * 40 — 10 rows, 40 pixels apart, top to bottom

The dot size is 4 + row * 2: row 0 → size 4, row 9 → size 22. Larger dots toward the bottom give the illusion of a flat surface receding upward.

Sample Code

import turtle
monty = turtle.Turtle()
monty.speed(0)
monty.hideturtle()

for row in range(10):
    for col in range(10):
        x = -180 + col * 40
        y = 180 - row * 40
        dot_size = 4 + row * 2
        monty.penup()
        monty.goto(x, y)
        monty.dot(dot_size, 'steelblue')

What Do You Think Will Happen?

The grid is 10 columns × 10 rows. How many dots will be drawn in total? Make your guess — then click Run to find out!

Try It Now

▶ Run ↻ Reset

10 × 10 = 100 dots. Were you right?

How It Works

monty.dot(size, color) draws a filled circle centered at the turtle's current position — no begin_fill() needed.

monty.penup() before goto() is essential here. Without it, Monty would drag a line from dot to dot across every row.

The size formula 4 + row * 2 is a linear mapping — it converts the row index (0–9) into a pixel size (4–22). This pattern of converting one number range to another appears constantly in data visualization.

Explanation Table

Line	What it does
for row in range(10)	Outer loop — 10 rows
for col in range(10)	Inner loop — 10 columns
x = -180 + col * 40	x position: left-to-right, 40px apart
y = 180 - row * 40	y position: top-to-bottom, 40px apart
dot_size = 4 + row * 2	Dots grow 2px larger each row
monty.dot(dot_size, 'steelblue')	Draw a filled circle in one line

Learning Check

Your Turn — Add Size Variation

The program below draws 100 dots but they are all the same small size — no depth effect! Fix the dot_size line so the dots grow larger toward the bottom of the grid.

▶ Run ↻ Reset

Change dot_size = 4 to dot_size = 4 + row * 2 to make each row 2 pixels larger than the row above.

Experiments

1. Map size to column instead of row. Change dot_size = 4 + row * 2 to dot_size = 4 + col * 2. You'll know it worked when dots grow larger left-to-right instead of top-to-bottom.

2. Change the color. Replace 'steelblue' with 'tomato' or 'mediumseagreen'. You'll know it worked when the dot color changes across the grid.

3. Color by row. Create colors = ['navy', 'royalblue', 'steelblue', 'cornflowerblue', 'skyblue', 'lightblue', 'lightyellow', 'yellow', 'orange', 'red'] and use colors[row] as the color. You'll know it worked when each row has a distinct color.

4. Shrink the gap. Change col * 40 and row * 40 to col * 20 and row * 20 — and increase the range to 20. You'll know it worked when 400 tiny dots fill the canvas.

Fantastic Work!

You used dot(), nested loops, and a size formula to create a grid with visual depth — the same technique used in data visualizations to encode a third variable as dot size! Up next: Color Wheel Wedges — dividing the circle into 12 slices of pure hue.