We can use positive numbers and negative numbers to represent temperature and elevation.

When numbers represent temperatures, positive numbers indicate temperatures that are warmer than zero and negative numbers indicate temperatures that are colder than zero. This thermometer shows a temperature of -1 degree Celsius, which we write $\text{-}1^\circ \text{C}$.

A thermometer positioned horizontally and with the bottom of the thermometer on the left, is labeled “degrees Celsius.” There are 4 evenly spaced large tick marks. Starting on the left, the large tick marks are labeled negative 5, 0, 5, and 10. Between each large tick mark, there are 4 evenly spaced small tick marks. The thermometer is shaded, starting from the left, up to negative 1.

When numbers represent elevations, positive numbers indicate positions above sea level and negative numbers indicate positions below sea level.

We can see the order of signed numbers on a number line.

A number is always less than a number to its right. So $\text{-}7 < \text{-}3$.

We use absolute value to describe how far a number is from 0. The numbers 15 and -15 are both 15 units from 0, so $|15| = 15$ and $| \text{-}15| = 15$. We call 15 and -15 opposites. They are on opposite sides of 0 on the number line but the same distance from 0.