2.2 Digitize line - LUPMISManual

2.2 Digitize Line

Level of expertise required for this Chapter: Beginner; general Map Maker training

The standard process to enter lines to GIS is to digitize on-screen, with a background map (or the source) displayed on screen, and to follow each bend (vertex) with the entry device (mouse). The line begins and ends at so-called nodes.

Before you start digitizing lines in Map Maker from orthophotos or scanned topo maps, you have to load the source map in the background: Right-mouse > Project manager > Add layer > Select file type (e.g. TIF or ECW) > Select folder and file > OK

Zoom in to the area of interest (by + and -), you can move around with the arrow keys (left, right, up, down). It is recommended to use to a very detailed level (see also  Chapter 1.2 about navigation).

Start digitizing: Line-tool (at toolbar left, or right-mouse > Drawing > Line) > Cursor changes to line with ‘Line’ > Start digitizing by clicking the mouse on each bend (creating vertices).

At the end of the line, you click the right-mouse > Line window: OK

You are ready to digitize the next line.

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If you like to modify a digitized line: Edit-tool (at toolbar left) > Double-click on the vertex (red dot), and drag it, or delete it. (See also  Chapter 2.5 for editing).

If you like to move the entire line (‘dragging’, recommended only in exceptional cases), you can do so by moving the square at the right bottom to a new location (see  Chapter 3.9 for full description).

After finishing all lines in that layer, you have to save it: Right-click (alternatively, main menu > Edit) > Save live layer > Accept DRA as file type > Select folder > Enter file name

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When you digitize a network, i.e. a road network, all lines have to ‘fit’ to each other: The end vertex point of one line has to be exactly (!) at the same location as the start vertex point of any other line(s). You can not do this just by moving the pointer to this location. You have to take one of the following tools:

A) ‘Snap vertex to nearest vertex’ after finished digitizing or editing the line: Line window or Edit vertex window: Actions > Snap vertex to nearest vertex > OK

B) If you have a new junction with a new road meeting an existing line,

it is easier to define an ‘overshoot’ (extend beyond the line to join) and then

Main menu > Edit > Show Selection Manager > Select-tool (at toolbar left) > Select the two lines to intersect > The Selection Manager window should show the two lines, like this:

Actions > Tidying > Tidy line junctions (spaghetti processing) > Tidy line junctions window: Snap distance: 0 m > Close gaps: 0 m > OK > X and

Select the ‘overshoot’ and delete

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Lines can also be added from:

• Google Earth (only large scale), as explained in  Chapter 5.4.8
  

• GPS tracks, as explained in Chapter 5.1.6, downloading in Chapter  5.1.7 (and  5.1.8)
• Field survey with conventional methods, as explained in  Annex 16.