There are three different types of surface mounted door closer mounting we usually see in the industry today.  Many of today’s door closer come packaged Tri-Pack, meaning they have the ability to work in  all three mountings, and they come with all the plates and arms to make this possible.    The three types of mounting are Regular Arm, Parallel Arm, and Top Jamb Mounting.  The first is Regular Arm.   Regular Arm mounting is when the door closer is mounted on the door, on the pull side of the door.  When the door is closed the arm would stick out from the face of the door at a 90 degree angle.  We usually see this type of mounting on interior doors.   An example of the Regular Arm mounting can be seen on our website.   The second type of mounting is Parallel Arm mounting.   With Parallel Arm mounting the door closer is mounted on the door, on the push side of the door.  The arm is parallel to the door when the door is closed.   This type of mounting is usually used on door the swing to the exterior.  An example of the Parallel Arm mounting can be seen on our website.  The last method of mounting surface mounted door closers is Top Jamb.   On a Top Jamb mounted door closer the hydraulic cylinder is mounted on the door frame, and the arm attaches to the door.   On a Top Jamb door closer the arm would stick out at 90 degrees from the door when the door is closed.   An example of a Top Jamb mounted door closer can be seen on our website.   My advice if you are looking for a replacement door closer would be to get the same model or version of what you have already, if you are unsure, I would check out out Door Closer Information Page and find a door closer with the same hole spacing.