This Article Provides A Detailed Description of The Regional Modeling Formalism Within A Rectangular Domain. This Approach Called Regional Rectangular Harmonic Analysis (R-RHA), Could Be Particularly Useful For Utilizing, For The First Time, Data From Malagasy Repeat Stations That Have Been Reoccupied Since 1983. Existing Regional Modeling Techniques Are Not Well Suited For Madagascar, As They Typically Require A Large Amount Of Data To Be Applied Correctly. However, Madagascar Has Only 25 Repeat Stations In Total, And Not All Of Them Are Reoccupied During A Magnetic Survey. The Results Obtained Using The Optimal Parameters Of The Rectangular Model Confirm Its Validity For Madagascar. Its Reliability Remains Limited To Areas Covered By Measurements. Even Though The Dataset Is Not Extensive, At Least One Measurement Is Required At Each Of The Following Stations : Antsiranana, Mahajanga, Toamasina, Toliary, And Taolagnaro. The Lack Of Data From Any Of These Regions Would Prevent The Proper Development Of Magnetic Maps Of Madagascar Using This Formalism.