The amount of insolation received is maximum at the equator. It goes on reducing with higher latitudes and is minimum at the poles. This is because in low latitudes the Sun's rays are direct and have to travel a lesser extent through the atmosphere. Hence, the heat of these rays is more intense. But in higher latitudes, the Sun's rays are slanting and have to pass through a greater extent of atmosphere. Hence, these rays lose heat on the way and minimum insolation occurs at the poles.