The two orbital elements that determine the size and shape of a planetary orbit are: planet's equatorial diameter and rotation rate tilt of the planet's axis and orbital period planet's orbital eccentricity and semi-major axis planet's speed and inclination

planet's orbital eccentricity and semi-major axis

Explanation:

The eccentricity and the semi - major axis controls the size and  shape of the orbit of the planet  . The value for the semi major axis is equal to the half of largest diameter of the elliptical orbit .

The eccentricity controls the shape of elliptical orbit . It is the ratio of the center to the focus ( sun ) length and the semi - major axis length .