Tutorial 7: Adding Features and Editing Line and Polygon Layers

Transcription

1 Tutorial 7: Adding Features and Editing Line and Polygon Layers Tutorial Content 7.1. When should I use a line layer to represent data? 7.2. How do I add line features? 7.3. How to use the snapping tool? 7.4. How to Extend and Trim Lines 7.5. When should I use a polygon layer to represent data? 7.6. How do I add polygon features? 7.7. How can I edit existing line and polygon data layers? Open your saved tutorial map project Lines We are now going to create a polyline shapefile. Lines shapefiles should be used when digitising linear features, such as watercourses and roads. Create a new polyline shapefile using the ArcCatalog tab. Tutorial 5 covers how to create a new shapefile. In this example we will digitise some circulation routes: major roads, minor roads, and footpaths. In this case the shapefile has been called Circulation. Remember to set the co-ordinate system for your new shapefile. Select Polyline in Feature Type. Your new shapefile should be automatically added to your open mxd project. Zoom in on an area of the map and start an edit session for the circulation layer. Make sure you select the Circulation feature template in the create features panel, remember that you might required to create a Feature Template. OS map data Crown Copyright/database right Try digitising some of the roads using the Line tool from the Construction Tools panel at the bottom of the Create Features window. You can choose between different types of line in the Editor Toolbar, such as Straight Segment, End Point Arc Segment, and Mid-point. You could add information to the attribute table to differentiate between for example, major roads, minor roads, and footpaths. 1

2 7.2. To add a line. Use the Create Features panel (Organize Templates window) in case you require to create a New Template for the Circulation shapefile. (See tutorial 6). Select the Straight segment line tool from the Editor toolbar. Click on the point you wish to begin the polyline, and then click wherever you need to add a vertex (change direction). Double click to end your line. You might need to change the layer symbology to make your lines thicker, so that you can see them more clearly Snapping OS map data Crown Copyright/database right Some of the roads meet at junctions. Here we want polylines to touch. To do this we need to use the snapping facility in ArcMap. Click on Editor, in the Editor toolbar and select Snapping... then Snapping toolbar. From the Snapping Toolbar, clicking each of the buttons on the toolbar turns on or off snapping to; points, ends, vertexes and edges respectively. There are more options from the snapping drop down menu. Keep all 4 snapping options on. Note: you can dock toolbars in the grey area at the top of the map display or at the edges. Just click on the toolbar and drag to the new location. Now when you hover near to the line that has already been digitised the cursor appearance will change. The square indicates that the pointer is within the snapping tolerance and will jump to the Endpoint of the existing polyline in this case. Click the mouse to add the vertex. OS map data Crown Copyright/database right You can change the snapping tolerance by clicking on Options in the Snapping drop down menu. The higher the value (pixels) the further the mouse pointer can be from a vertex or edge and still snap to it. You can also change whether the layer name or snapping type is shown from the options. 2

3 7.4. Extending and Trimming Lines To extend or trim a line in ArcMap, you can use the Extend or Trim tools on the Advanced Editing toolbar. This is accessed from the Editor drop down list, More Editing Tools, Advanced Editing. Extend Tool Trim Tool OS map data Crown Copyright/database right An Ordnance Survey/EDINA supplied service. Select the Edit tool from the Editor toolbar. Click on the feature that you want to extend your line to so that it is selected. Click on the Extend Tool and double click at the end of the line that you want to extend. The selected line will automatically extend to meet the other line. Trimming works in the same way. Select the line you want to trim to. Then click on the Trim Tool and double click on the part of the line you want to trim off. 3

4 Other Line Options in ArcMap There are other line options in ArcMap, which you may find useful for tasks such as sketch design. You can set the length of a line feature within ArcMap. To do this, create the first vertex of your line. Then right click and select Length from the drop down menu. Type a value in the text box that appears and press Enter on the keyboard. Note: the value is in map units. In our case each map unit is a metre. OS map data Crown Copyright/database right If you move the pointer now, the line is restricted to the length you typed in. You can set angle for the new vertex, using the option for Direction. You can also use existing line features and create parallel or perpendicular features Polygons Polygons should be used where you need to record information about areas, such as field boundaries, land uses and vegetation cover. Create a new polygon shapefile in ArcCatalog to show field boundaries. Select Polygon as a Feature Type. In this case the shapefile has been called Field_Boundaries. Start an Edit Session, clicking on the Field_Boundaries shapefile in the Start Editing window. Remember that you might to create a New Template in the Create Features window for the Field_Boundaries shapefile. Make sure Field_Boundaries is selected in the Create Features panel. The polygon tool will automatically be selected. Click on the map display to start the polygon. Click again to add a vertex. Double click to finish the polygon. 4

5 We want the next field boundary to join onto the polygon that we have just created. To do this we can use the snapping facility. Open the snapping toolbar from the drop down menu in the Editor toolbar Try digitising one of the adjacent field boundaries using the polygon Tool. The new polygon should now snap to the edge and corners of the one we have just drawn. You might want to change the layer symbology in the Symbol Selector. In this example the Fill Color has been set to No Color and outline colour has been set to red. The outline width has also been increased to OS map data Crown Copyright/database right Editing tools. Splitting Polygon Features Start an Edit Session. Use the Edit Tool to select the polygon you want to cut or split, so that it is highlighted blue. Select the Cut Polygons Tool from the Editor toolbar. Create a line that bisects the polygon where you want to split it. To start the line click with the mouse. To finish the line double click. The polygon will automatically split along the line you created. This example shows a polygon being split with a simple line. You can also add vertices to change direction, by clicking with the mouse. 5

6 Advanced Editing Options An Ordnance Survey/EDINA supplied service. A number of other editing options can be accessed using the Advanced Editing toolbar in ArcMap including: copy, trim, extend, intersect, fillet, explode. To open the toolbar, select More Editing Tools in the Editor drop down menu and then Advanced Editing from the drop down menu to the right. OS map data Crown Copyright/database right An Ordnance Survey/EDINA supplied service. Editing Vertices (Lines and Polygons) Start an Edit Session. Select the feature that you want to modify (lines or polygons) with the edit tool. Click on Edit Vertices in the Editor toolbar. The Edit Vertices toolbar will open and the vertices of the selected feature will be displayed. An Ordnance Survey/EDINA supplied service. To move a vertex, hover over the vertex until the mouse pointer changes to a box with four arrows, then click, hold down and drag the vertex to its new position. The feature will be updated once you have saved the edit. To delete a vertex, you can select the Delete Vertex icon in the Edit Vertices toolbar, and select the vertex you want to delete. Alternatively whilst using the edit tool you can hover over the vertex you want to delete, and right click with the mouse. Select Delete Vertex from the drop down menu. 6

7 To add a vertex, you can select the Add Vertex icon in the Edit Vertices toolbar, and click where you want to add a vertex. Alternatively whilst using the edit tool you can click on a line or polygon at the point you want to add a vertex, and right click with the mouse. Select Insert Vertex from the drop down menu. An Ordnance Survey/EDINA supplied service. Editing a Shared Edge If your shapefile uses adjacent polygons which share an edge, then it might be necessary to edit a shared edge. To do this, start an Edit Session. Select More Editing Tools in the Editor drop down menu and then Topology from the drop down menu to the right. The Topology toolbar will open, select the map topology icon. The Map Topology window will open. Tick the box next to the layer name with the shared edge that you want to edit. Click OK 7

8 Zoom in to the shared edge that you want to edit and select the Topology Edit tool from the Topology toolbar. Click on the shared edge. It will be highlighted in purple. You can now edit the shared edge in the usual way. An Ordnance Survey/EDINA supplied service. 8