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6.4. GIS Book: Working with lines

To digitize lines, select the required layer in the Create Features panel (e. g. road_network). In the Construction Tools section, click Line as shown in Figure 17. To draw the line, click on the starting point and then follow point to point until a section is completed (e. g. a railway).  To end the line, double-click on the last vertex or press the F2 key. The green nodes indicate the number of points that have been marked to construct the polyline; the red node is the last marked point. The procedure is repeated for all sections of the shapefile (e. g. the entire road network).

When digitizing lines, it is important to maintain connectivity between elements. For example, in the case of the road network, you cannot have sections that do not connect to each other, nor sectors where the connections go beyond the borders of an existing entity. In order to be more accurate in editing and avoid errors, Snapping tools (Customize > Toolbars) allow the pointer to automatically adjust to the edges, vertices or other nearby geometric elements within a given degree of tolerance.Practice: For the water_network layer, identify the riverbed in Figure 4, then proceed with digitizing in the same way as with the road network.

Figure 17. Line digitizing in ArcMap

To modify a polyline, select the Edit Tool () icon in the Editor toolbar. Then click on a segment, which give it a light blue color. You can now delete the line or move the entire line. If you double-click on the required segment, all the vertices of the polyline will be shown. Each of the vertices can then be moved freely until the desired path is obtained (Figure 18).

Figure 18. Modification of polylines

It is recommended to avoid placing too many vertices in a straight line; it is feasible to place only vertices at the end points. In the case of a curvature, more vertexes are needed to fit the shape. To delete a vertex, right click on it and then select Delete Vertex. To add one or more vertices right click on the polyline segment and select Insert Vertex. In some cases, a polyline needs to be divided into two or more parts.

To do this, select the polyline and with Split Tool (), located in the Editor toolbar. The line is divided with a click on the required point (which is highlighted in red). 

To delete a line completely, select the line with the Edit Tool and press the “Delete” key. To select two or more lines, press the “Shift” key.

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