and I have a lot of this problem like in image. The two line are separated but i want a continuous line. What rule should I choose in Topology Checker? I want to know all the separated line, so i can fix them.
[GIS] How to connect lines with gaps to continuous line
qgistopology
Related Solutions
I think this is correct behavior. In logical (network) topology all lines must end (or start) at the end (or start) of another line. You have to physically split lines at the location (vertex) where other line touches. You can visualize this as water pipes. If you need to create T join on existing pipe, you have to split that pipe first, then add fitting and then connect another pipe to fitting. I hope that sound clear. This behavior led to another problem - one logical entity divided to multiple pieces. So you ends up with many features with same attributes, which is not good for maintenance. Imagine you need to change river name... Now you have to change it for each corresponding segment. Often this is not big deal. But if you want to solve this elegantly, you can model rivers as two separate tables (feature classes). One with attributes only and one with geometries. Attribute table will hold unique list of all rivers. Geometry table will hold river segments and one extra attribute(say id_river) with relation to river attribute table. In this setup one river can have multiple geometry segments, but you maintain only one river record.
To get rid of the red markers that show topology errors, uncheck the box at the bottom of the Topology checker panel that says show errors:
Best Answer
Use the Must not have dangles rule, and if lines are always supposed to meet end to end rather than having an end just touch another line anywhere, use the Must not Intersect or Touch Interior. All line ends that do not meet another line end will appear as a topology error and with the topology tools you will have the option to snap, extend or trim dangle ends, or split lines that touch or cross other lines. Snap would work best for the line pair you showed. Where your lines actually should terminate in a dangle (such as cul-de-sacs and stubs in a road network), you can mark those dangles as an exception so they will no longer show up as a topology error.
See the topology rule illustrations and explanations in this help topic.