The Mativir drains significant areas of the Ihtimanska Sredna Gora mountain range.

The river takes its source under the name Baba in the western part of the Ihtimanska Sredna Gora at an altitude of 963 m, some 1.3 km west of the village of Borika.

In the first 2 km it flows north and then turns eastwards passing through a deep forested valley.

At the confluence between the Baba, the Razhana and the Meshkovitsa at 693 m, now under the name Matnitsa, the river turns southeast and after 3 km it enters the Ihtiman Valley.

At 2 km north of the village of Mirovo it turns northeast, exits the valley and enters the Sersemkale Gorge between the ridges of Belitsa to the northwest and Eledzhik to the southeast, both part of Sredna Gora.