This up-to-date map of the inner solar system shows Mercury, Venus, Earth and Mars cyan or white squares, and their orbits are represented by the blue ellipses around the sun (the yellow dot at the center). The Earth is highlighted because of its special importance to us. Small green points mark the location of asteroids which do not approach close to the Earth right now. Yellow objects (with the exception of sun) are Earth-approaching asteroids which are called Amors after the first one discovered. Amors have orbits which come close to the Earth but they don’t cross the Earth’s orbit, yet.
Finally the red boxes mark the location of the Apollo and Aten asteroids. These cross the Earth’s orbit and are the most directly identifiable astronomical threat for the near future.
It is estimated that there are perhaps 100,000 to 1,000,000 undiscovered asteroids on similar Earth crossing orbits.