INTRODUCTION TO GIS WORKSHOP EXERCISE

Transcription

1 111 Mulford Hall, College of Natural Resources, UC Berkeley (510) INTRODUCTION TO GIS WORKSHOP EXERCISE This exercise is a survey of some GIS and spatial analysis tools for ecological and natural science research. You will explore your GIS data, create a new shapefile, do simple geoprocessing analyses, and create and export a map. The data you will be using for this exercise can be found in C:\Workspace\Moorea\Tahoe. You will be using this folder throughout this exercise, and will often be referred to as your working folder. These are important points that you should read before you go any further! These are informative tips that may help you in the future! You will be working with the following datasets that are available for free at (all except for the samples and the water quality data which is fictitious). All data is in UTM Zone 10, NAD 27 = projection is Universal Transverse Mercator (UTM) Zone 10, and datum is North American Datum (NAD) More information can be found through the metadata links on the website listed above. GPS_locations.dbf DBF file containing GPS coordinates you collected in the field. There are three fields: sample ID, Easting (which is the X- coord), and Northing (which is the Y-coord). water_quality.dbf DBF file containing water quality measurements you collected in the field. There are four fields: sample ID, ph, water temperature (Temp), and dissolved oxygen (DO). 24k_roads.shp (shapefile format) Line shapefile containing roads. 24k_hypso.shp (shapefile format) Line shapefile containing hypsographic contours, which are elevation contours. Hydrography.mdb (geodatabase format) Geodatabase, which contains two polygon datasets: Rivers_24k and Lakes_24k (Note that these were originally shapefiles when downloaded from the USGS; I converted to geodb to give you practices using them.) soils.shp (shapefile format) Polygon shapefile containing a soil map surveys. census.shp (shapefile format) This is a polygon shapefile containing 1999 census data including population densities and other data. nlcd_tahoe.tif (TIF format) National Land Cover Dataset of the Tahoe Region. The spatial resolution is 30 m. dembathy (GRID format) Digital Elevation Model (DEM), including bathymetry of Lake Tahoe. The spatial resolution is 10 m. dem_hillshade.jpg (Georeferenced JPEG format) Hillshade created from the DEM and bathymetry. The spatial resolution is 10 m. DRG_24k.sid (MrSID format) Digital Raster Graphic (DRG), which is basically a digital USGS topo map. landsat321.tif (TIF format) Landsat 7 satellite image of the Earth s surface around Lake Tahoe. Only the red, green, and blue bands are provided here, but you can download all bands at the website above. The spatial resolution is 30 m.

2 There are also some layers in the data folder with _symbology.lyr as part of the name. These are pre-set symbology for certain layers. Add Data 1. Open ArcMap 10 from the desktop icon, or by going to Start All Programs ArcGIS ArcMap.. 2. Click Cancel when the Getting Started Window appears to start with a A New Empty Map Then, click on the Add Data button 3. In the Add Data window, click on the Connect To Folder button: 4. Navigate to C:\Workspace\ Moorea\Tahoe, and click OK. The folder s contents should appear in the window (below).

3 5. Add all of the following layers to ArcMap: dem_hillshade.jpg dembathy DRG_24k.sid landsat321.tif nlcd_tahoe.lyr To select more than one at a time, use the Ctrl key on your keyboard. The data layers are added to your Table of Contents and appear in your Map window. Check off and on the boxes to the left of the layer name. Experiment with moving the layers in different orders (shown at the right). You can also collapse and expand a layer s legend using the toggle switch.

4 6. Click Add Data button again, and add the following data layers: 24k_hypso_symbology.lyr 24k_roads_symbology.lyr soils_symbology.lyr If a little red exclamation point appears next to the layer, and the layer doesn t appear in the map, it is because the link between the.lyr file and the shapefile is broken. Simply click on the red exclamation point, and navigate to the correct file. These layer files contain stored symbology for certain shapefiles. Notice that in the Table of Content list, it doesn t say _symbology.lyr That is because each symbology layer is linked to its shapefile. 7. Click Add Data button again, and add the following data layers: census.shp Lakes_24k (inside Hydrology.mdb) Rivers_24k (inside Hydrology.mdb) 9. Once you ve added all the files listed above in the folder, go to the File Save. Or Click on the Save icon: Since ArcMap has been known to crash, it is a good idea to save your work regularly. For this exercise, name your.mxd project something unique, with your name in it, and save it in the Tahoe directory. Use the zoom and pan tools, the identify tool, and the find tool to explore and browse the data. Zoom in Pan Fixed Zoom in Zoom Back Select Pointer Measure Distances Find XY Locatiopns Zoom out Full Extent Fixed Zoom out Zoom Clear Forward Selected Identify Find Change the layer properties 1. Right-click on the layer: Lakes_24k. A context menu appears Stop for a minute and look at the options in this context menu This menu is very necessary in ArcMap for several reasons: 2. You open the layer s attribute table by clicking Open Attribute Table 3. You can zoom to the extent by clicking Zoom To Layer 4. You can export the layer to another layer by clicking Data Export Data 5. You can change how the layer looks and acts under Properties 2. Choose Properties to open the Layer Properties. The Layer Properties dialog appears. Each layer has its own Layer Properties. 3. Click on the General tab. Change the Layer Name to something clear and concise this revises the way the Layer List, or Table of Contents, looks in ArcMap, and consequently the map legend later in the exercise. It does not, however, change the name of the data file.

5 4. Next, click on the Symbology tab. Click the symbol selector button, and change the symbol to a more appropriate one. Optional: For even more symbols, click on the More Symbols button to bring up a list of additional symbol sets. You can also click Properties and fine-tune your symbols even more!

6 5. In the soils layer properties, click the Display tab, and change the transparency level to be 75%. This allows for better viewing of multiple layers on top of each other. 6. Next, go through all of your layers, and give all the layers appropriate names, symbols, and labels. Experiment! For example, try playing with transparency of elevation and/or hillshade for a 3D effect (below).

7 Create new point shapefile with GPS coordinates Many times we have an Excel or DBF spreadsheet with GPS coordinates, field sample data, or other information on it that we want to put into a GIS. 1. Click the Add Data button: 2. Add the GPS_locations.dbf to ArcMap. Right-click on GPS_locations.dbf in the Layer TOC, and choose Display XY Data In the Display XY Data dialog, choose Easting for the X Field and Northing for the Y Field. The Coordinate System should automatically recognize that we are NAD_1927_UTM_Zone_10N, but if it does not, you can set it manually by clicking the EDIT button, and search for NAD_1927_UTM_Zone_10N. You ll then have to click to open each folder until you see the result that can be selected. Search here Click through folders and select the result

8 The result is a GPS_locations Events layer listed in the TOC. 4. Right-click on this Events layer and Zoom to layer. Since this is an Events layer, and not a permanent dataset, we must save it. 5. Right-click again on the Events layer, and go to Data > Export Data 6. Save your new GPS locations as a shapefile called GPS_Points.shp in the working directory. Click Yes to add your new shapefile to your project. You can now remove the Events layer if you wish. You have now created a GIS shapefile from your spreadsheet with GPS coordinates! One last step: at the top of the Layer TOC, you will see several icons : List by Drawing Order, List by Source, List by Visibility, List by Selection, and Options. The purposes of these are for Drawing Order (the layer names, TOC order, etc.), for source (so you can see where datasets are located on your computer), and for selection (so you can easily make a layer selectable or not). You will not be able to change the drawing order while in source mode.

9 Join a table to a shapefile Next, you want to join water quality data that you collected in the field to the GPS_Points shapefile you just made. 1. Add waterqual.dbf to your project. 2. In the TOC, Right-click on GPS Points layer, and go to Joins and Relates Select Join 3. In the Join Data window, choose to Join attributes from a table, and choose ID as the unique identifier in both the GPS Points shapefile and the waterqual.dbf (these must match one-to-one, or a proper join won t work!) 4. Click OK. If you are asked the question about whether to build an index, Click Yes. This just helps speed up the connection between the two datasets. 5. In the Layer TOC, right-click on GPS_Points and click Open Attribute Table. Before the join, the only fields were ID, Easting, and Northing. Now you have additional water quality fields (OID, ID, PH, TEMP, and DO) from the waterqual.dbf. These new fields are circled on the following page.

10 You can perform joins with data in Excel, Access, or other spreadsheet or database files, whenever you want to attach, or join the data to the shapes in the shapefile. In order to make these water quality fields a permanent part of GPS_Points, you must perform one last step. 7. Close the attribute table, and right-click on GPS_Points, and go to Data > Export Data and save the dataset as a new shapefile called GPS_Points_WaterQual.shp. Explore the Attributes 1. In the Layer List, right-click on the GPS_Points_WaterQual points layer, and choose Open Attribute Table The attribute table for the GPS_Points_WaterQual points layer opens. An attribute table is a database file (similar to Excel) that has a record for each feature of the layer, whether it is a point, line, or polygon. These data are called attributes.

11 Move the attribute table so that you can see both the lake map and the table. 2. Click on the row heading of any random GPS point in the attribute table. The row is highlighted, or selected, as is the corresponding geographic point. This is how the geographic and tabular data are linked. 3. Under the Selection icon in the Layer TOC, right click GPS_Points_ WaterQual, and choose Make this the only selectable layer Then click on the select tool in the toolbar and draw a box around several points in the middle of the lake (pictured below). Note that in ArcGIS 10, you can also select by Polygon, Lasso, Circle, or line.

12 To clear selected features, click the button. 4. Click on the Table Options button in the attribute table, and choose Select by Attributes In the window that appears, build a query for points that have low dissolved oxygen, by following the steps below: a. Double-click on DO (may also be called waterqual.do ) b. Single-click on < c. Click on Get Unique Values. All the unique values for DO appear. d. Double-click on 8.6 This is how to build a query. Build more queries, finding out where other high or low levels of ph or temperature exist! Click Apply. Notice that some samples on the edges of the lakes are selected. Interesting how the edges of the lake have the lowest dissolved oxygen! (see picture below) In ArcMap, whenever one or more features in a layer are selected, any task/tool/process you run on that layer, it will ONLY be processed on those particular selected features (and not all the features in the layer).

13 When you are done querying the data, go to the Table Options button and click Clear Selection. This will unselect all selected points. 5. Calculate statistics on a column. Open the attribute table for GPS_Points_WaterQual if it is not already open. a. Right-click on the TEMP field column name, and choose Statistics (Note: you can only run statistics on numerical fields!) b. The results appear, along with a frequency distribution of the values. You can use the field drop-down menu to view statistics for any numerical field in the attribute table.

14 6. The Summarize tool is useful for polygon datasets, where you want to summarize a numerical variables across categories. a. Open the attribute table for the soils layer. b. Right-click on the field column heading for MUNAME, and choose Summarize The Summarize window appears, where you can summarize the characteristics of any other field for each unique MUNAME. c. Check the Minimum, Maximum, Average, and Sum for the AREA. Sum is important as it s the total area covered by that soil type. Min. and Max. are important as it define the range of patch size. Average is important because it describes the average patch size. Count is also calculated, which tells the number of patches for that soil type. d. Click OK, and then click Yes to add the table to your project. e. The Sum_Output.dbf is added to your Layer TOC. Right-click and Open the table.

15 Perform Simple Spatial Analyses 1. Clip the census layer to the extent of the other layers. You may have noticed that the census layer includes more land than our study site consists of. We want to CLIP the census layer to match the other layers. a. In ArcToolbox, go to Analysis Tools Extract Clip, and double-click on Clip. b. For the Input Features, choose the census layer. c. For the Clip Features, choose the soils layer. d. Use the button for Output Feature Class to choose the folder and name for your output. Give your new clipped census layer a name, such as census_clipped.shp. e. Click OK. The clipped census layer is added to the Layers TOC. You can now remove the previous unclipped census layer. The CLIP tool is very useful for clipping large datasets down so that it only encompasses your study site!

16 2. Buffer your GPS points. a. In ArcToolbox, go to Analysis Tools Proximity Buffer. b. Choose the GPS_Points_WaterQual layer as the Input Features, and save the Output feature class to: C:\WorkSpace\Moorea\Tahoe\GPS_Buffer.shp c. Choose your buffer radius. The example below shows 1000 m buffer radius. d. Choose to Dissolve NONE so that there is a separate buffer for each GPS point. You can also try it with dissolved buffer too. Try it for lines and polygons too!

17 3. Calculate distance to Nearest river. a. In ArcToolbox, go to Analysis Tools Proximity Near. b. Choose the GPS_Points_WaterQual layer as the Input Features. c. Choose the Rivers layer as the Near Features. d. Choose your search radius. The example below shows 10 *miles* search radius. The results are joined to the GPS_Points_WaterQual layer. Open the table to view for each GPS point the River feature ID ( NEAR_FID ) that is closest and how close it is ( NEAR_DIST ). All of the entries should have values. A value of -1 indicates that there were no features within the given search radius.

18 4. Calculate a surface showing road density. This function uses the Spatial Analyst Extension. Before proceeding, verify that this extension is activated by going to Customize Extensions in the File drop down menu. You will see a list of available extensions, be sure that Spatial Analyst is checked active before closing. a. In ArcToolbox, go to Spatial Analyst Tools Density Line Density. b. Choose the Roads layer as the Input Features. c. Choose the RD_ID as the Population field. Save the output raster to: C:\WorkSpace\Moorea\Tahoe\road_density.tif d. Choose an output cell size of 500 m. e. Choose a search radius of 10,000 m.

19 3. Interpolate a surface water quality concentrations. There are many interpolation algorithms you can choose from. a. In ArcToolbox, go to Spatial Analyst Tools Interpolation Natural Neighbor. b. Choose the GPS_Points_WaterQual layer as the Input Point Features. c. Choose the DO as the Z value field. Save the file to: C:\WorkSpace\Moorea\Tahoe\DO_interpolate.tif d. Choose an output cell size of 100 m. Try it again with different interpolation algorithms, and with the other water quality parameters.

20 Create a choropleth map 1. Go to the Layer properties for your clipped census layer. 2. Under the Symbology tab, choose to show Graduated colors under Quantities (see below). 3. Choose to show the Value of TOTPOP (Total Population), in order to see if population has an effective on DO or ph through pollution and nutrient loading. Any numeric characteristic can be mapped using choropleth maps. They are very common for displaying census data.

21 Create graduated symbols 1. In the Layer Properties of the GPS points shapefile, go to the Symbology tab. 2. In the left-hand side panel, choose to show Graduated symbols (under Quantities). 3. Choose which field to use as the Value with which to populate the graduated symbols. 4. Change the symbol size range, the symbol template 5. To change the classification scheme, click Classify and open the Classification dialog. Otherwise, click Apply to see the results on your map. In the Classification dialog, you can change the method of classification (to represent the graduated ranges differently), and the number of classes. Create a map Switch over to Layout View, by either clicking on the little icon for the Layout View on the bottom-left of your map window, or by going to the View menu Layout View. Zoom in Pan Zoom to 1:1 Fixed Zoom out Zoom Forward Zoom out Full Fixed Extent Zoom in Zoom Back Percent Shrink to Fit

22 Notice that your Layout Toolbar is automatically added. The Layout Toolbar has navigation tools (zooming, panning, etc.) for the layout map, not the data view map. This is the big difference between the data tools and the layout tools. This can take some getting used to at first: you use the data tools in the data view, and the layout tools in the layout view. 1. To insert a legend, go to the Insert menu Legend Follow the wizard through step-by-step to make the legend look the way you want it. Re-size your map area to make room for the legend, if you prefer. 2. To insert text, a north arrow and a scale bar, go to the Insert menu, and choose what you want. Note: ArcMap places your map elements in the center of your map at first, and you have to move them to where you want. So look carefully when you ve added an element sometimes it s hard to see them in front of your map! The legend is linked to your Layer List if you change a name or symbol in the Layer List, the legend is updated!

23 Export your map 1. Go to the File menu Export Map... and change the Save as type to PDF. Use a unique name, with your name in the name. Click Options to change the output resolution. 300dpi is a high quality output resolution for printing (below).