GEOG2113: Geographical Information Systems Week 7 Mapping Hazards & Threats Practical Task

Transcription

1 GEOG2113: Geographical Information Systems Week 7 Mapping Hazards & Threats Practical Task Theme: Mapping a zombie outbreak! Key datasets & sources: ITN Network (road network) Location of Defence Research Centre (shapefile) Background mapping (OS 50k JPG) Key skills we will learn or develop in this session: Use of the Network Analyst Use of the Buffer Tool Key tasks we will undertake during this session: 1. Set up our GIS for using Network Analysis (part 1) 2. Use Network Analyst (part 2) 3. Use Buffer Analysis (part 3) This week we will be using GIS to map the progress of a zombie outbreak from the Defence Research Centre in Malvern and calculate how long it would take the zombies to reach the University of Worcester. We will explore two key types of spatial analysis for this purpose: (1) network analysis, and (2) buffer analysis. We have done some research which suggests that on average, zombies travel at a speed of 2km per hour. The zombies have just escaped, so you had better get started

2 Part 1. Setting up the GIS Download all the data for Week 7 from Blackboard. Open ArcMap and save your map to the desktop or the drive you are working from. Remember to save every so often so you don t lose any work. Add all the data from Blackboard Within the ITN_Network dataset, switch off all layers except ITN_NetworkDataset in the table of contents. This should correspond with the road layout shown on the underlying OS map. If you can t see the road layout vector, you may need to swap the layer order in your table of contents, make the lines a darker colour or make the OS mapping slightly transparent (Right click > Properties > Display). Select Toolbars from the Customize menu Select Network Analyst and the Network Analyst tool bar should appear, as shown below. If you cannot find Network Analyst, or you get a license warning error, or once loaded the toolbar options are greyed out, then you will need to add in this toolbar. This can be achieved by selecting Extensions and checking the box next to Network Analyst.

3 On the Network Analyst toolbar click the Show/Hide Network Analyst Window icon (box with a little blue flag). The Network Analyst window should then open up adjacent to your Table of Contents. So now the Network Analyst toolbar should be all set up and ready to go

4 Part 2. Using Network Analysis to Map the Dispersal of Zombies! Click the Network Analyst dropdown on the left-hand side of the Network Analyst tool bar and select New Service Area. A New Service Area analysis layer will be added to your Table of Contents and your Network Analyst Layer Window. Now we have set up the Network Analyst, we need to tell the GIS about the important datasets we want to use. First of all, we need to identify the Defence Research Centre as the source of the zombie outbreak (this is located in Malvern, Worcestershire). Right click Facilities in the Network Analyst Window, and select Load Locations. Choose to load from the Defence Research Centre shapefile, leave all other settings as default and click OK. In the Table of Contents, make sure you are displaying your data by drawing order, and not by source. To correct this, click the List By Drawing Order button. Then right click on Service Area in the Table of Contents. Then select Properties > Analysis Settings.

5 We now want to tell the analysis tool that the zombies will be dispersing from the Defence Research Centre at a speed of 2km per hour. This is equivalent to o Impedance: Length (m) o Default Breaks: 2000 Once you ve entered these values, leave the remaining settings as they are and click OK. Next, to process this scenario right click on Service Area in the Table of Contents and select Solve. Wait a while for the analysis to run and a coloured polygon should then appear on your map. This represents the spatial spread of the zombies after a period of 1 hour (or over a distance of 2000m/2km) since they escaped from the Defence Research Centre. We now need to repeat these exercise to determine how far the zombies will have got after o 2 hours (4000m or 4km) o 3 hours (6000m or 6km) o 6 hours (12,000m or 12km) o 8 hours (16,000m or 16km) To do this you need to start at the beginning of Part 2 again, by creating a new service area and loading the Defence Research Centre as Facilities Location each time. Follow through all the other steps to create polygons showing how far the zombies have travelled after each of the above time periods. Make sure you show the different time periods using different colours, by altering the symbology (right click on the polygons layer > Properties > Symbology). You may need to play around with the order of the different Service Areas to ensure the polygon of zombie dispersal for each time period can be easily seen. Eventually you should have a map that looks something like this

6 Question: How long (approximately) did it take for the zombie outbreak to spread to the University of Worcester?

7 Part 3. Using Buffer Analysis to Map the Dispersal of Zombies! So far, our analysis has been focused on the road network as the routes the zombies would use. But imagine if zombies could fly. Next, we re going to use buffer analysis to see how far the zombies could fly from the outbreak centre using straight line distances. In the Table of Contents, move the Defence Research Centre shapefile to the top of the drawing list (if it s not already there), so it is clearly displayed on your map. Using the Search Tool (right hand side of your screen), we now want to search for the buffer analysis tool. Type buffer into the search field, and select Buffer (Analysis). Within the buffer tool dialogue box, select or input the following options: o Input Features: Defence Research Centre shapefile. o Output Feature Class: Navigate to your preferred location and give the new output buffer a sensible name so you can easily identify it (e.g. Zombie_Buffer_2km.shp) o Linear unit: (this is the straightline distance the zombies will have travelled) 2000 o Units: Metres o Leave all other options unchanged and click ok. After a few moments, the tool should output your new buffer shapefile, which shows how far the zombies have flown across the map, which should look like this:

8 Repeat the use of the buffer tool to create shapefiles for the following distances too: o 2 hours (4000m or 4km) o 3 hours (6000m or 6km) o 6 hours (12,000m or 12km) o 8 hours (16,000m or 16km) You should end up with five circular polygons radiating out from the Defence Research Centre, showing the progress of the flying zombies. Question: How long (approximately) did it take for the flying zombies to spread to the University of Worcester when we used the buffer analysis? Question: How does this length of time compare to our calculations for the Network Analysis tool in Part 2? Question: What would be the disadvantages of using buffer analysis for a walking zombie outbreak? Would it give us an accurate indication of the time it would take the zombies to reach the University?

9 Question: Thinking about some of the datasets that are used to map the real hazards we have talked about today (e.g. landslides, volcanic eruptions, floods), what other information do you think we might we need to assess the hazard of, exposure (or vulnerability to) and risk of a zombie outbreak properly?