# Model Geometry

MARE2DEM uses a right-handed coordinate system with the *z* axis
positive down. *x* is the model strike direction where conductivity is
invariant, so \({\sigma} = {\sigma(y,z)}\).

Note

There is no assumption about where \(z=0\) resides in the model or
data spaces, although generally it is recommended to set \(z=0\) to
be sea level. Similarly, transmitters and receivers
can be located at any *x* position, but generally they should be close
to \(x=0\).