I have read several tutorials and questions here on this site, but I have some lingering questions/doubts that I would like clarified.
My project is tracing roadways from a 1926 map so that I can compare infrastructure then and now. I have successfully georeferenced my 1926 raster map onto a contemporary shapefile, reduced transparency, etc. I have enabled freehand line editing, which is the best way to accomplish this task, it seems. My map has two kinds of roads shown that I want to trace: the paved roads, and the unpaved roads (marked by full, bold lines and staggered, broken lines). So, then, here is what I would like clarified.
- In the New Vector Layer box, an option is given for Name, Type, Width... I have named the feature line 'roads,' which is relevant for question #2. What exactly is the Type option (text data, whole number, decimal number, etc.) for, what is it not for, and could someone give a quick example of when this option might be useful?
- When I trace with the freehand edit tool, I realize that when I unclick, several points/nodes/features (whatever they are called!) are placed along the traced line as if I clicked them each individually. OK... so there appears a popup box asking me for 'id' and 'roads'--'id' is blank, and 'roads' is 'NULL.' What exactly is going on here with this? So far, I have simply left the box as-is and clicked 'OK.' Would I regret this later if I wanted to edit the lines or something? What is the point of this box, the information in it, and how is it useful?
- The paved roads I want to trace are not connected to each other--some paved roads in the north, south, etc. So far, what I have been doing is tracing a line of paved roads as described above, and then moving my location in the map to do the same in the north or other areas. Following this procedure as described, will all the lines traced be counted/recognized as the same feature/network of feature? Is it alright to trace a road coming into a city from one direction, unclick, and then trace the road coming into the city from the other direction, and will it still be part of the same road?
- How do I trace the unpaved roads once I get the paved roads all traced? (I suspect that I would need to allow for this when creating the new shapefile layer from the start, by adding a 'roads' AND another thing like 'unpaved roads,' is this correct? But if I have not done this from the beginning, am I screwed and should start over?)