A birth chart or natal chart is a representation of the planets in the sky at the time of birth of a person. It depicts the rising sign orlagna & position of planets in different zodiac signs (or rashis) & houses. The four directions in the birth chart are Poorva (or East), Paschim (or West), Aakash (Zenith) & Paatal (Nadir). North & South are not shown in it because the Earth rotates on it's axis from West to East, due to which the zodiac signs & other planets seem to be moving from East to West in the sky. North & South directions don't play any significant role.
In any chart Mercury or Budh can't go more than 2 houses away from Sun or Surya. Similarly in any chart Venus or Shukra can't go more than 3 houses away from Sun or Surya. Rahu & Ketu will always be present 7 houses apart.