Concept 2 of 6
Street Maps: Line Relationships
Today's big idea
Parallel never meet, perpendicular meet at 90°, intersecting cross any other way.
Three pairs: never meeting, meeting square on, and crossing at a slant.
How it works
👀 What's going on?
Look at any street map and the same three arrangements keep turning up. Two roads that never meet, two that meet square on, and two that cross at a slant.
💡 Here's the trick
Look at the three pairs above. Parallel lines never meet, however far you stretch them. Perpendicular lines meet at exactly 90°, making a square corner. Intersecting lines cross at any other angle. Every perpendicular pair is intersecting too, but only the 90° ones earn the special name.
🪄 How to do it
- 1.Ask whether the lines ever meet, which is how the picture above splits them first.
- 2.If they never meet, they are parallel.
- 3.If they do meet, check the corner. Exactly 90° is perpendicular, anything else is just intersecting.
✍️ Try it
Think about the two long edges of a ruler, then the hands of a clock at 3 o'clock. What is each pair?
The ruler's long edges hold the same gap forever, so they are parallel. At 3 o'clock the hands make a square corner, so they are perpendicular. Those hands are intersecting as well, since perpendicular is a special kind of intersecting.
⚠️ Watch out
You might be thinking two lines that look like they will not meet must be parallel. Parallel means the gap never changes at all. Two lines a hair off parallel still cross, just a very long way off the page.
🌟 Why this matters
Builders check walls are perpendicular so the doors fit their frames. Shelves get hung parallel so nothing slides off one end. Getting it wrong is how a bookcase ends up leaning.
Exam tip: A drawn into a corner of a figure is the standard mark for 90°.
Watch me solve one
Quanta solves it
“Watch how I think through one of these — then you try.”
THE PROBLEM
“Train tracks run side-by-side and never touch. What are they?”
- 1
Look at the gap
The tracks stay the same distance apart everywhere.
- 2
Do they ever meet?
Never. That's the key clue.
- 3
Match the type
Never-meeting same-distance lines = parallel.
- 4
Answer ✓
Train tracks are parallel
Now you try one — same steps, different story 👇
See it in action
⚡ Time to play!
Tap each road type to learn its definition. Explore all 3 to unlock the question!
Quick check
✅ VERIFICATION
Two roads cross at 40°. What is that pair called?
⚡ Finish the activity above first to answer.
Keep going!
Up next: The Meeting Point
Count corners and sides in any polygon.