A portable radio-frequency identifier (RFID) reading terminal can comprise a microprocessor, a memory, an RFID reading device, and a display. The portable EIR terminal can be configured, responsive to successfully reading a plurality of RFID tags attached to a plurality of items sustained by a physical structure, to group the plurality of read RFID tags into zero or more clusters, by correlating quantities of RFID tags read within several time periods to spatial positions of the coverage shapes of the RF signals transmitted by the RFID reading device during the several time periods. The EIR terminal can be further configured to determine the spatial positions of the RFID signal coverage shapes based on the spatial positions and orientations of the portable EIR terminal during the several time periods. The EIR terminal can be further configured to display a quantity of RFID tags within each cluster overlaid over an image.