Verification of segment maps

[jorgegil]

In the verification of segment maps, the same topology and geometry tests as for axial maps should apply, but using the current tool short lines, small lines and islands returns too many false positives. Could it be a GIS data accuracy problem due to projection? Test for:

• orphans
• islands
• overlapping lines
• duplicate lines
• dangles
• short lines (disconnects)
• invalid geometry

User would have to indicate if input is segment or road centre line, as some checks might differ.

[chiaramartinuzzi]

I would like to know what the error "invalid geometry" consist of and how should I solve it during the stage "verify layer". If I select an invalid geometry in the errors list, it doesn't show me the problem in the screen.

[jorgegil]

‘Invalid geometry’ are mal formed features according to the GEOS standard. Those are not recognised by QGIS and therefore they are not displayed on the map and you can’t zoom to them. However, the entry is highlighted in the attribute table and you can check there what it is and eventually delete it.

• Usually these are incomplete geometries from data entry mistakes in some other software.
• They can also be geometries that were copy/pasted between tables with different CRS.
• Finally, they can be entries in a data table with attributes and NULL geometry.

QGIS has a geometry check tool/plugin that can be used to identify and sometimes fix those geometries.