How robot localization package make transformation from map to odom

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I am relatively new to ROS and i'm using robot localization package for my project. I wonder how exactly ekf_localization node do the localization, even though i haven't set any transformations from map to odom yet. Does the node automatically make the transformation for you or am i missing something?

I'm intending to use magnetometer for map frame orientation and i wonder how can i transform that orientation to my odometry frame.