This article presents the problem of searching useful magnetic anomalies by using the magnetometric survey methods. Metal debris (spot anomalies) often create local interference that makes it difficult to find vast spatial anomalies caused by the remnants of ancient buildings, such as walls of houses, wells, dugouts, etc. The main purpose of this study is to develop an algorithm that eliminates such interference. We explore the methods of working with magnetometric data and design an algorithm which is based on seeking spot anomalies and using the arithmetic method of smoothing spatial data. We test the final algorithm on many real datasets, obtained during excavations in the Crimea, and it shows good results.