In this paper we present a novel indoor localization approach in Wireless Sensor Networks (WSN) which is based on spatial reasoning by observing the relationship between RSSI (Received Signal Strength Indication) values from spatially distributed data sources. In this work a WSN is applied as the environmental supervision system in containers during the transport processes. The proposed positioning approach exploits the simple straightforward movement of the “palette-accompanying” sensor nodes, which are arbitrarily distributed in palettes during the loading process. The target sensor nodes are capable of reasoning their loading route and end position by collecting and comparing the RSSI readings from the distributed anchor nodes. Since no numeric distance determination with RSSI is required, the typical ranging error due to the instability of the signal strength is avoided and the calculation complexity is reduced. The test results show that the localization accuracy fulfils the requirements of the sample applications.