7.03.04 Buffering Tutorial

Mon, 11/19/2007 - 13:32
Disclaimer: The objective of this tutorial is to get familiar with the GIS software. The tutorial only covers some parts that are being done In a real analysis. The results that are being displayed in the tutorial can’t be compared with the results a real analysis would generate.IntroductionThe objectives of this exercise are to arrange layers properly and to use the buffer wizard to create a buffer. The scenario is to prepare an analysis based on right of way for existing and planned electrical transmission lines and try to identify eventual conflicts to existing land-use, urban areas in particular.
1 Getting started
1.1 Open ArcMap. Select the A New empty map option.
1.2Click on to add the IS17_Tl2007 (transmission lines) layer to the work space. It is found in C:/ CLUP_EXERCISE_DATA/02_IS/ folder. Click Add. Also add some base map features from the C:/ CLUP_EXERCISE_DATA/00_BM/ folder such as barangays_bndry, Lake and Roads. To identify conflicts with residential/urban areas we need to add a land use layer. Add the LM01_ExiLu2007 layer from the /04_LM/ folder.
1.3 Rename the IS17_TI2007 layer to Transmission Lines. To do this, right-click on the layer in the table of content, select Properties. The Layer Properties window opens. Go to the General tab and type the new name in the Layer name field. (See image below.) Click OK. (You can also click on the layer in the table of content and type the new layer in the table of content without opening the Layer Properties window.)
1.4 Also rename LM01_ExiLu2007 to ‘Land use’ and barangays_bndry to ‘Barangay boundaries’. (Repeat step 1.3 on these layers.)
1.5In the menu bar click File > Save As… to save a map document as buffering_v1 in /CLUP_EXERCISE_DATA/06_Workfolder/. Don’t forget to save your progress now and then throughout the exercise.
2 Applying Symbology
2.1First of all arrange the layers in the following order (from top to bottom): Transmission lines, Roads, Barangay boundaries, Land use and Lake. Simply drag the layers in the table of content so that they are positioned in the correct order.
2.2Open the Layer Properties window (refer to step 1.3 if you forgot how to do this) and go to the Symbology tab for the Transmission Lines layer. See image below. At the left, click on Categories and click Unique values, many fields. Then choose TL_VOLT from the first Value Fields list menu and TL_NAME from the second Value Fields list menu. Click the Add All Values button.
2.3Uncheck the symbol for . Place the cursor over the words TL_VOLT, TL_NM in the Label-column. Click once. You can now edit the label to ‘Voltage (kV):’. In the same way rename the label for 230, Planned 2008 to ‘230 (planned’). Delete the comma after 69, 230 and 500. Click Apply.
2.4Now right-click on 500 (in the Value column), select Properties for selected Symbol(s). The Symbol Selector window will open. (see image below). Click More symbols and select Forestry. To the left, search and select the T23 Pipeline 2 symbol. Choose width 9,00. Click OK.
2.5(Back in the Layer Properties window, click Apply if you want to update the map.) Repeat step 2.4 on the other categories (other voltage). Use the same symbol but the size ‘7,00’ for 230 and 230 (Planned) and size ‘5,00’ for 69. Click Apply.
2.6To be able to separate the planned distribution lines from the already existing ones, open the Symbol Selector window for 230 (Planned) once more. Click Properties. The Symbol Property Editor window appears. In the Layers box at bottom-left, select the line symbol (see image below).
2.7Select Simple Line Symbol from the Type list menu. The settings in the window changes to Simple line. From the Style list menu, select Dotted, as seen in the image below.
2.8Click OK and OK again.
2.9Now go to the Symbology tab in the Layer Properties window for the Land Use layer. Click Import. The Import Symbology window opens. Select the first option "…from a layer file” and browse for landUse.lyr (found in /LM_04/ folder and click Add. Click OK in the Import Symbology window. The Import Symbology Matching Dialog window opens. Select ELU_TP from the Value Field list menu. Click OK. If this worked well the Symbology tab should now look like in the image below. If it didn’t work out, follow the procedure as in step 2.2 but select only Unique values and assign symbols based on the ELU_TP field (refer to 4.21.03 for proper color coding).
2.10As you can see in the map, and from the order of the layers in the table of content, the Barangay boundaries layer covers the Land use layer (the nice palette in the land use layer cannot be seen in the map). Now, assign proper symbology for the Barangay boundaries layer – that is no fill-color (select No color and Boundary, neighborhood as outline symbol (click Properties in the Symbol Selector window and Outline in the Symbol Selector Editor window). A tip! Since you don’t need to categorize the symbology as in step 2.2-4 here, use this shortcut: Simply double-click on the symbol next to the layer’s name in the table of content, and the Symbol Selector window will appear right away. Assign the proper symbology from here.
If you add a polygon layer such as land use/coverage or built-up areas, this should be at the bottom. Then, polyline layers such as roads and rivers can be displayed atop on the polygon layer. This is also the reason why we assigned no fill-color to the Barangay boundary layer – the boundaries will now be shown atop of the other layers, whereas the barangays’ areas (or more correct: surfaces) will be completely transparent.
2.11Verify that your layers are in a correct order (so that all features are displayed properly) and also have proper symbology. To change the order, simply drag each layer up or down in the table of content. See image below.
3 Creating a Buffer
From the map we can see that the proposed new power line will cross through urban areas and it could be interesting to analyze the negative impact on existing urban settlements. The next step is therefore to do the buffering. Creating a buffer provides a visual representation on the map of the area within a certain distance of one or more features. We can also use the buffer to select features in other layers that fall within the buffered area..
3.1In the menu bar click Tools > Customize. The Customize window opens (see image below). Go to the Commands tab and select Tools in the Categories box at the left. Click the Buffer Wizard icon in the Commands box to the right. Drag the icon and drop it in the Toolbar. Click Close.
3.2Now click the Bufferd Wizard icon that you just dropped in the toolbar (). The Buffer wizard window appears (see image below). Select The features of a layer. In the list menu below, select Transmission Lines. Click Next. [/b].
3.3Refer to the image below. Select At a specified distance and type the distance. The buffer for a 500 kV transmission line is 65 m. Select Meters from the Distance units arelist menu. Click Next.
3.4Refer to the image below: Select Yes to Dissolve barriers between. Select In a new layer. Specify output shapefile or feature class. Click on to define the output folder /CLUP_EXERCISE_DATA/06_Workfolder/ and type the filename ‘Transmission_lines_buffer_65m’. Click SavE then Finish.
3.5Change symbology on the Transmission_lines_buffer_65m layer to a hatching symbol. You are now done with the exercise. The result will look something like this (zoomed in a bit where the planned transmission line starts):
It seems that the alignment of the will cause impact on substantial parts of the urban settlements. If an aerial photo or a cadastre dataset would have been available it would have been quite easy to point out what lots/parcels that will be affected. Maybe it is a good idea to try an alternative route for the new transmission line?
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