Rocket spins the big globe in the library. Blue whirls past, then brown, then more blue.
"There is so much water," he says. "Is the whole planet an ocean with a few islands?"
Raven stops the globe with one finger. "Not quite. What do you notice about how much is blue?"
Nova projects a flat map of Earth onto the library wall. "Here is a clue," she says. "Scientists have measured it. Guess first, then we will check."
About 71 percent of Earth's surface is covered by water. That is a little less than three quarters.
Maps help us find land and water features: mountains, volcanoes, valleys, ocean floors and deep trenches.
A topographic map shows the shape of the land. It uses contour lines.
A contour line connects places that are the same height above sea level.
| Feature | What it is |
|---|---|
| Mountain | land that rises high above the area around it |
| Volcano | an opening where lava, small rocks and steam erupt |
| Ocean trench | a long, narrow dip in the deep sea floor |
| Continent | one of Earth's big land areas |
Every point on one contour line is the same height above sea level.
Each line stands for one height.
Mapmakers use contour lines to show bumpy land on flat paper.
| Statement | True or false? |
|---|---|
| More than half of Earth's surface is water. | ? |
| A contour line connects places with the same height. | ? |
| Maps can only show land, not ocean floors. | ? |
| A mountain rises high above the area around it. | ? |
Great mapping! Tomorrow we look for patterns in where mountains, volcanoes and earthquakes are.