# Topology

The topological editing capabilities of **Mapboard GIS** are a major step
towards iterative geologic mapping. When topological editing is enabled, unit
definitions snap to their enclosing linework, allowing the structure of the
map to emerge as mappers focus on capturing data.

In **Spatialite mode** and **Image mode**, the onboard Spatialite engine is used
to manage topological relationships.
The reference implementaion of topological editing capabilities
is the **PostGIS Geologic Map**
topology solver operating in **Tethered mode**.

**Spatialite** support for topology is
slower and more bug-prone than the **PostGIS** reference implementation.
The underlying algorithms will be improved over time. Please file issues
as needed to document unexpected behavior.

In both modes, the **Topology settings panel** manages whether topological editing is
active, and whether filled map faces are shown. During topological editing, each
change to the map results in a rebuild of the modified area. The **PostGIS Geologic Map**
engine is good at finding the minimum set of relationships to change, but the
**Spatialite** backend currently uses a less efficient algorithm.

Onboard topological solving is a complex, battery-draining
algorithm, and iPads have limited system resources.
**Real-time topological solving should be turned off during intensive field use
if stable power availability is a concern.**