Exotic Matter (XM) is needed to power your Scanner and perform tasks. You can collect XM (the mini-glowing blue dots on image) by moving through those areas. The XM will be automatically harvested by your Scanner when it is within your interaction circle/range.
If XM falls below critical levels, your Scanner will be disabled and visually indicated as such by a red screen. This can happen either by completely depleting your XM (too many tasks), or from an attack by a nearby portal.
Higher concentrations of XM are typically found by portals and commercial areas.