Introduction to GIS & Mapping: ArcGIS Desktop

Transcription

1 Introduction to GIS & Mapping: ArcGIS Desktop Your task in this exercise is to determine the best place to build a mixed use facility in Hudson County, NJ. In order to revitalize the community and take advantage of special loans, you want to build your facility in an area with at least 1.5 times the national unemployment rate (It was 4.4% as of August 2017). You will also explore what sort of railroad transit is available in this area. Open ArcMap 1. Before you begin, decide where you will be storing the GIS files that you will be downloading and creating in this exercise. You can create a working folder on the desktop or in the Documents folder. Copy the exercise data from the folder designated by the instructor, or download the exercise data from You will need to unzip the folder before you can access the data. 2. Open ArcMap (Start (Windows icon)) > All Programs > ArcGIS > ArcMap ). You will be prompted on whether you want to open a new map project, or an existing one. You should open a new map by selecting a blank map and clicking OK. All of the controls are dockable. You can also click on the thumbtack symbol to pin a window, such as the Table of Contents, to the screen, or unpin it so that it hides off to the side when you re not using it. 3. In the top area (toolbar), right click to see a list of additional toolbars you can easily turn on or off. You will find many options within ArcGIS by right clicking on different parts of the interface. 1

2 Add a basemap from ArcGIS Online Adding a basemap is a quick and easy way to provide context to other spatial data you are displaying or analyzing. 1. Click the dropdown arrow next to the add data button ( ). 2. Select Add basemap 3. Click on imagery and click add. Note that the layer is served over the web so it may take some time to draw (and that you have to be connected to the internet for it to continue drawing). What you see depends on the scale you are working in on your map - as you zoom in closer you will typically find more detailed information. Your scale is displayed in the Standard toolbar and automatically adjusts as you zoom in and out. To navigate your data you will primarily use these buttons: From left to right, they are used to zoom in, zoom out, pan, and zoom to the full extent of all visible data. Find and add data As you learned, there are many sources for GIS data. We will first find transportation data for New Jersey. 1. Go to: This shows all the open transportation data for New Jersey. We found this site by doing an internet search for new jersey gis data. 2. View the New Jersey Railroad Stations data layer by clicking on its name. Can you find the metadata? Can you tell how the dataset was created? 2

3 3. Navigate back to the main transportation data page and download the New Jersey Railroad Stations and Passenger Railroad Lines by clicking on the data layer name and selecting Download > Shapefile. If you want to explore any other data from this area, feel free to download it. 4. Move the data to your working folder and unzip each file by right clicking and selecting 7-zip > Extract here. 5. In ArcMap, click the Add Data button and navigate to your working folder. If you are adding data from a drive or folder that you have never before used, you may not see it listed. In this case, first use the Connect To Folder button ( ) to select and add the directory to your list of folder connections. 6. In addition to the transportation data you just downloaded, you will add census unemployment data to the map. Add the following layers: Hudson_county_nj_tracts_unemployment, New_Jersey_Railroad_Stations, Passenger_Railroad_Lines_in_New_Jersey. Ignore any warning messages you see. The US Census divides the country into continuous polygons and aggregates census data for these polygons before releasing the data to the public so that individual responses cannot be identified. Our data is for census tracts, which contain between 1200 and 8000 people total. 3

4 7. In the Table of Contents of ArcGIS (where all layer names are listed) turn the layers on or off using the checkboxes located to the left of each layer name. Leave the basemap layer unchecked for now so that the next few steps will go more quickly. 8. Adjust which layer draws on top by dragging layers above or below one another. You will want your rail stations and rail lines on top so they won t be covered by the census tracts polygons. If your layers will not drag, click the List by Drawing Order button at the top of the table of contents. Explore the attribute table 1. Right click on each layer and select Open Attribute Table. Every point, line, or polygon file has an attribute table. Any data in the attribute table can be used for displaying and labeling on the map and making queries. You can also create new columns in the table and add data or calculations. Metadata can be key to understanding attribute tables that use codes and abbreviations. 2. Leave the attribute table for the tract unemployment data open and scroll all the way to the right. Can you tell what any of the column headings mean? It s unlikely, so you will need to look at the metadata. Open the text file that is in your data folder. You now see the definition for each column. This data was downloaded from a database called Social Explorer, and joined to a polygon file from the US Census. Variable SE_T037_02 is the number of unemployed people in the civilian population. Is this what we want to map? Why or why not? Mapping raw numbers is usually not useful because the total population in one census tract may be more or less than another. One way to normalize the data is to take into account the total population and calculate a rate. 3. From the table dropdown menu, select Add Field. 4. Name the variable Unemp_rate and choose the type as double. Press Ok. 5. Right click on the new column that was added and select Field Calculator. Click Yes when you see the warning message. 4

5 We want to divide the number of people unemployed by the total number of people in each tract. Based on the metadata, which columns will you use? 6. Add fields to the equation by double clicking on them in the list. Make sure your equation matches this one: [SE_T037_02] / [SE_T037_00] and click Ok. We know that we want to find tracts that are 1.5 times the national unemployment rate. This is equal to.066 or greater. 7. Click the Select By Attributes button ( ) at the top of the table window. 8. Double click on Unemp_rate in the list. This will add it to the text box near the bottom of the window, where you are building your select by attribute expression. Finish the expression by setting it greater than or equal to.066 ( Unemp_rate >=.066). Click Apply. All rows that correspond to a tract with a higher than average unemployment rate are highlighted and the corresponding tracts are highlighted on the map. 9. Close the Attribute Table Export to a new file We will export the selected tracts to a new data layer so that we can more easily visualize which tracts have high unemployment. Exporting a smaller area of data is the easiest way to subset a dataset to only the desired records or keep your file sizes smaller and more manageable. 1. Right click the unemployment layer in the table of contents and select Data > Export Data. 2. Export the selected features using the same coordinate system as the layer s source data. 3. Click on the folder icon to view and edit the save location. Name the file unemp_high. Make sure that the Save as type is set to shapefile not file and personal geodatabases feature classes. 5

6 Note that file names and locations can be very important when working on projects. GIS software tends to generate many files, so you want to make sure to use file names that are descriptive and easy to remember in the future. 4. Click Save and OK then click Yes when asked if you want to add the exported data to the map as a layer. 5. Clear the selected features by clicking the clear selected features button in the top menu bar ( ). 6. Save your map document to the desktop or a working folder on your local drive using File> Save. Symbolize data Change a single symbol Rather than completely covering the unemployment polygon layer with the one for high unemployment, we can change the symbology of the high unemployment layer so that we can highlight the tracts and still see the tracts for the entire county underneath. 1. In the table of contents, double click the colored rectangle below the high unemployment layer (unemp_high) and change the fill to a pattern, such as 10% simple hatch. That way we can still see the unemployment tract data layer underneath. 6

7 Explore data distribution Before we make a choropleth map of the unemployment rate, we need to examine our data in order to create the most appropriate map. A quick way to explore the distribution of our data in ArcMap is to make a graph. For future projects, you will likely want to explore your data outside of ArcGIS in statistical software or data visualization software in order to better understand it. 1. Click View > Graph. 2. Choose Histogram as the type and Unemp_rate as the value field. Feel free to change the number of bins and see how the histogram changes. This histogram is showing the number of tracts (y axis) that fall into each unemployment range (x axis). Not all ranges are shown because of size constraints on the axis, but this still gives you an idea of the general shape of your data. We see that unemployment rate is relatively low, but that there are some outlying tracts with a high employment rate. 3. Change the Value field to the total civilian population in the labor force (check the metadata if you forget which variable this is). You can see that there is one tract with a lower population than the rest. The unemployment rate may not be as accurate for this location so we should examine it further. 4. Press cancel to close the histogram. 7

8 5. Explore the tract with a low population in the attribute table of the Hudson_county_nj_tracts_unemployment layer by opening the attribute table and right clicking on the column for Civilian Population in Labor Force 16 Years and Over. Select sort ascending. This one tract has a civilian population in the labor force of only 15, which is unusual. 6. Select this row by clicking on the grey box to the left of the beginning of the row. Close the attribute table. The tract will now be outlined on the map. 7. Turn on the basemap and turn the tract unemployment layer on and off so you can examine what is located in this area. It appears to be an industrial area and natural area, which may be why many people do not live here. With so few people, the unemployment rate is likely to be less accurate. You can keep this in mind when you are choosing a site for your facility. Make a choropleth map 1. Turn on the Hudson_county_nj_tracts_unemployment layer and double click its name. You can alternatively right click on the layer name and choose properties. This will bring up the Layer Properties window. 2. Click the symbology tab. 3. Change the symbology to Quantities: Graduated colors and select "Unemp_rate" in the Value Field. 4. Symbolize the data in whatever way you think is best. Map symbology can be used to alter the way people view and understand information, just like statistics. It is important to understand what you want to express in your map and how to best symbolize your data. a. Pick a color ramp from the drop down menu and b. Use the classify button to choose the number of classifications and type of classification method. If you don t remember how breaks are created for each method, refer back to the earlier lecture notes. You will see a distribution of your data similar to the histograms we created earlier, in order to help you choose a classification method. c. To reduce the number of decimals shown, click on Label > Format labels. 5. Click Ok when you are finished. 6. Save your map document to the desktop or a working folder on your local drive using File> Save. 8

9 Do you have an idea about where you might build based on the unemployment rate? Obviously many factors go into selecting a building site. We will examine one more: train access. Find tracts that have railroad stations You will use the Select by Location tool to select all tracts that contain a railroad station. 1. In the Selection menu at the top, click Select By Location. a. Select from the Hudson_county_NJ_tracts data layer. b. The source layer is the railroad stations and the selection method is contain the source layer feature 2. Click Ok. Now all tracts that contain a railroad station are highlighted in blue. This is temporary until you clear the selection. Choose a tract for building 1. Click the selection button ( ) at the top of the screen and click on the tract that you want to build in, based on the visualization you have made. This will clear all the other selections and only highlight this one parcel. You can select more than one tract by holding down the Shift button. 2. Export the selected feature using the same method you used above so that you know which location(s) you selected to build on. 3. Clear the selection ( ) once you have exported the layer. 4. Make final changes to the color of any of the data layers. Create a layout of your map 1. On the main toolbar menu at the top of ArcMap click View > Layout View. 2. Click File > Page and Print Setup to choose either portrait or landscape orientation. Click OK. 3. Click on any part of your map. Adjust the data frame (area in dotted blue lines) to fill most of the page but leave room for a title, scale bar, etc. 4. On the main toolbar click Insert > Title, and choose a title. 5. Insert a legend using the same menu, include the appropriate layers you want in your legend, click next until you complete the legend dialog screens, and arrange the legend on your page so it fits with the map. 6. Insert a North arrow in the same menu, and choose one of the many options. 9

10 7. Insert a text box to add your name, date, and sources for your data. You can also insert a larger variety of textboxes that allow you to change their background color, by using the draw toolbar (right click in the toolbar and select it if it is not currently displayed). 8. Change the scale of your map by zooming in or out or typing in a desired scale in the top toolbar and notice the scale bar automatically updates. Export your map 1. Click File > Export Map 2. Choose PDF in Save as type. Note that if you save as an AI (Adobe Illustrator), the layers will remain as separate, editable layers in Illustrator. If you save as JPEG or TIFF, you can adjust the resolution of the exported file. 3. Open your map in Adobe Acrobat to see what it looks like. Save your ArcMap document 1. Click File > Save from the top menu bar. Note that when you save an ArcMap document, you are only saving a link to the layers in your project. If you move your project to a new location, you will need to move all the files linked to your project with it. Each shapefile has multiple files associated together, and they need to stay together to work properly! By default, ArcMap stores the full path name to each layer in the ArcMap document. This means that if you move your files around, your path name will change and you will need to redirect ArcMap to the new file location for each folder of data. If you will be moving files around, it is recommended that you save a relative path to the data files in your project. 2. Go to File > Map Document Properties, and check the Store relative pathnames to data sources box. 10