Pixelated Paths

Posted August 30, 2016 by turtle
maze image from wikipedia.org

Original author

Project GUTS, excerpted from Adventures in Modeling (Colella, Klopfer and Resnick)

Resource type

Content area

Use type



Learning how to build a StarLogo TNG model requires learning how to translate an initial idea of what the turtles should do into a precise description of how they should do it. In this Activity, participants start by drawing a path, then develop a description to help others recreate the path without ever seeing it.  Later we will draw a direct analogy to the conditional instruction used in programming the same behavior.

Students will gain a basic understanding of a conditional statement and see how conditional statements can be used to give precise directions on what to do in response to certain conditions.   Students will also be introduced to the idea of absolute vs relative perspectives.

Materials needed: 

  • Grid paper and tracing paper (or transparency sheets)
  • three colors of pens (black, red, and blue)
  • White board (or large post-it pad) and markers

Running the activity

Give participants a sheet of graph paper and ask that each of them draw a path on the paper. The path should consist of a series of straight lines, connected at right angles. It will be easier for participants to complete the next step of the Activity if they draw lines in the middle of the squares on the graph paper, instead of on top of the preprinted lines. They should also indicate the beginning of the path (with a turtle pointing in the starting direction of the path) and the end of the path.

Next, each participant will create a set of “landmarks” to help someone else re-create the path, without ever seeing it. Have participants place tracing paper (or a transparency sheet) on top of their graph paper, and mark the starting position and direction of the turtle on the tracing paper. Then participants should create colored landmarks on the tracing paper (not directly on the grid paper), telling the turtle where to go according to following the rules:

  • If you see a black square, then turn all the way around (180°).
  • If you see a blue square, then turn left (90°).
  • If you see a red square, then turn right (90°).

The goal is to place enough landmarks so that the turtle will follow the entire path from beginning to end.

  1. Have each person exchange tracing paper (not the original path) with a partner. Each partner should follow the landmarks indicated on the tracing paper and draw the turtle’s path directly on the tracing paper, without consulting the author or the original path. The turtle should begin walking straight ahead from the starting point, turning whenever it bumps into a landmark. The goal is for the turtle to reach the end of the path just by following the rules.
  2. When all participants have finished, ask them to compare the tracing paper paths with the originals.

Concluding the activity:

Conclude the activity by asking the following questions:

  • How many people were able to accurately follow their partner’s path?
  • Were there any silly mistakes? (Did some people forget certain color blocks or use the wrong colors?)
  • What strategies resulted in the most successful path followings? (Larger color blocks, simpler paths, predictable patterns?)
  • What would happen if people drew curvy paths? What other rules would make it easier to follow these paths?
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