GIS Basics for Urban Studies

Transcription

1 GIS Basics for Urban Studies Date: March 21, 2018 Contacts: Mehdi Aminipouri, Graduate Peer GIS Faciliator, SFU Library Keshav Mukunda, GIS & Map Librarian Librarian for Geography 1

2 1. Finding demographic geospatial data in SimplyAnalytics: In this section, we will find and export geospatial data from socio-economic datasets for Vancouver, using the SFU Library resource SimplyAnalytics. SimplyAnalytics visualizes data using choropleth maps (graduated colour), which are thematic maps where areas are shaded or patterned in proportion to the value of the statistical variable being displayed. It is an easy way to visualize how a measured value varies across a geographic area. From lib.sfu.ca do a Library Search for SimplyAnalytics and select it from the search results under Databases. In SimplyAnalytics, select the Data tab. In the search box, type in household median income and from the search results select Households by Income (Current Year). These are estimates based on the last census data and various other factors. Next, search for labour force unemployment and from the search results select Household Population 15 Years or Over by Labour Force Activity Unemployment Rate. Now close the search results window, and select the Locations tab. Search for Vancouver and select Vancouver, BC (CSD) to get data at the census subdivision level. The variables now appear on a choropleth map. On the top right-hand side of your screen, click on View Actions and select Export shapefiles. 2

3 In the options window that opens, make sure to select Dissemination Areas as your geographic unit, and select both median household income and unemployment rate data variables. Put in your address, and click Send. The shapefiles will be ed to you. When you ve downloaded the files, they can be added to a new ArcMap document where you can do more analysis. We re not going to look at these datasets at this time, but remember that SimplyAnalytics is an excellent source of Canadian geospatial data, especially for demographics (census), psychographics, and business information. Instead, let s now look at how to use ArcGIS, which is an industry-standard GIS application. 2. ArcGIS: Introduction to ArcCatalog The purpose of this exercise is to give you an introduction to ArcCatalog. ArcCatalog is an application for managing geographical data within ArcGIS. It is used to copy, move and delete data; search for data; preview data before deciding whether to add it to a map; and to create new data. It also contains tools for creating and viewing metadata (information about spatial data, such as who created it, date of creation, its accuracy, and so forth) Data The data for this exercise is available in a folder in SFU Vault: goo.gl/1rccjr - Create a new folder on your Desktop and name it GIS-Workshop. - Copy the data from the SFU Vault folder to the folder you just created on your desktop and use WinZip to unzip the files Opening ArcCatalog Double-click with the left mouse button on the ArcCatalog icon from the Windows Start menu, select Programs > ARCGIS > ArcCatalog After opening the software, you will see a window like this one: 3

4 The left side of the screen lists a set of possible locations for data in the Catalog Tree. Don t worry if yours does not look exactly the same. It is easy to add directories for data by clicking on the Connect to folder icon on the top left toolbar. 1- Click on the Connect to folder icon and make a connection to the folder you created on the Desktop. From the catalog tree on the left side, navigate to your connected folder. You will see a list of shapefiles. The.shp extension of the file means that these files are in shapefile format (points, polylines, and polygons) and thus can be read by ArcMap. Although this is not the only file format ArcMap can read, it is a popular format. Note: Shapefiles are a combination of 3 to 7 individual files that make up one shapefile. Always use ArcCatalog to copy/cut paste shapefiles into different folders. 4

5 2- After making the folder connection and locating data, it is possible to preview the data before adding it to ArcMap. Click once with the left mouse button on Park.shp and then select Preview tab on the right side of ArcCatalog screen. You may want to explore the data a little bit more by using the tools provided on the main toolbar. You can use the to zoom in, to zoom out and pan the data. 3- Alternatively, you can switch the display from Geography to Table to view the attributes associates with the geography. Geography Now switch to Table to explore the content of the table. You can find the total number of records at the bottom of the table. 5

6 Table 3. Introduction to ArcMap The aim of this exercise is to give you an introduction to the basic principles of ArcMap. Basic functions of the program will be explored, such as loading data ( shape format), zooming and panning in a map, and the relationship between geographic features and non-geographic attributes will be demonstrated Opening ArcMap - ArcMap can be opened from multiple locations. This time, we will open it from ArcCatalog. It can also be opened from the start menu or an icon on the desktop. From ArcCatalog, click on the ArcMap icon: Upon opening ArcMap you will see the following startup window: 6

7 This is a new feature with version 10 of ArcGIS software that allows you to make a shortcut to your most-used data location. Since we re just beginning, we are going to skip this option and simply use the default. Click on Blank Map or Cancel. Now you will be in a new, blank document in ArcMap. This area is known as the Map Display. This display area is where map features are drawn Adding data through ArcCatalog: There are two main ways to add data. We will begin with adding vector data obtained from the district of North Vancouver GeoWeb Portal from ArcCatalog. 1. Click on the ArcCatalog tab icon at the top right of the display. You will see the catalog tree. 2. Navigate to the data you want to add. For us, that is under Folder Connections: C:\Desktop\GIS-Workshop 4. We will add the following shapefiles: BusStop.shp, Creek.shp, DangerousGoodsRout.shp, Lake.shp, Park.shp and TransmissionLine.shp. You can drag and drop the files into the Table of Contents under Layers. 7

8 5. Now go to the Add Data button and from the drop down menu, select Add Basemap > Imagery Adding data through ArcMap: In addition to ArcCatalog, we can add data directly through ArcMap. 1- Select the Add Data button. If you selected the drop-down, choose the first option, Add Data. Or from the menu bar, select File > Add Data > Add Data. Notice how most of the button and tool bar functions are available to us now. Also notice the scale display next to the Add Data button. This display tells you what the scale value is of the current view. If it displays the value 1: 37,159,239 that means that every one unit on the map is equal to 37,159,239 units in the real world. As you zoom in and out of the map the scale will change dynamically. Scale is an important concept in computer mapping. The scale of the map often determines the amount of information that can be shown without the map becoming too busy. 8

9 Also notice the position display at the bottom right of the screen. As you move the cursor around the view these units change dynamically according to your cursor s position. Your map units are likely in meters Moving around with map display: Now we examine ways of zooming in and out and panning. The Tools toolbar contains eight buttons that provide zooming functions and allow you to define a custom view of the layer data. Some of the most useful ones are illustrated here. Zoom in Zoom to previous extent Zoom out Full extent Pan 4. Handling Spatial and Tabular Data: 4.1. Purpose: The aim of the exercise is to deepen your knowledge of attribute tables. You will learn to import data from an Excel worksheet, convert a list of coordinates to a shapefile, and create simple SQL-queries Data: The data that we are going to use for this exercise has been downloaded from the District of North Vancouver Open Data Portal. You will create a map that contains bus stops, transmission lines, parks, transportation routes for dangerous goods, and lakes. Open ArcMap. When ArcMap is open, you see the ArcMap Getting Started dialogue box in the main application window. This dialogue box allows you to quickly start a new map or open an existing map or template. On the Getting Started dialogue box, under the Existing Maps section, click Browse for more. 9

10 On the ArcMap Document dialogue box, browse to your desktop folder where you downloaded the data. Click DNV_Map.mxd, as shown in the graphic and click Open. 10

11 When the map document is open, observe the display area, the toolbars and the table of contents on the left Importing a Table ArcMap can handle different types of tabular data formats, such as text (*.txt), dbase (*.dbf) and Excel worksheet (*.xlsx). For this exercise, a table that contains geographic coordinates (X and Y) of transmission towers has been provided for you. Navigate to your desktop folder where you downloaded the data for this workshop and add Transmission Towewrs.xlsx by clicking. At the moment, it is just a table, not yet linked to a layer. That means you cannot display its contents visually on the map. If you want to be able to show the transmission towers on the map in the Data Frame, each feature must be connected to a geographic feature Create Features from Table Data with X, Y Coordinates 11

12 Every transmission tower has an x and y coordinate. In ArcMap, you can easily create a point layer from these coordinates listed in the table (Transmission Towers.xlsx). This option is very useful when working with point data, for example, taken with a GPS. In order to add XY data to a map in the data frame, right-click the table name and select Display XY Data. Leave everything as default and Click OK on the Display XY data. If a warning message regarding the missing Object-ID field is displayed, it is safe to ignore it and click OK. Check the added XY data in ArcMap. A new layer, Transmission Towers$ Events, has been added to the Table of Contents. Convert point data to shapefile: To turn this theme into a real shapefile and not just a temporary layer as it is now, it must be converted to shape format. Right-click on the Transmission Towers$ Events in the Table of Contents and choose Data >Export Data and an Export Data dialog box will appear. Choose to Export: All Features and name the Output feature class, Transmission Towers and save it in your working folder with the rest of your data. Click OK. A new layer will be created and saved. When you are asked: Do you want to add the exported data as a layer? Click Yes. 12

13 Now the transmission towers are added as a new shapefile (point layer) to your map document. Change the symbol and represent the towers with a proper shape and color Making Queries (SQL) SQL (Structured Query Language) is a query language to select and retrieve data from an attribute table. SQL in ArcGIS is done with the Select by Attributes option. In the Select by Attributes dialogue box you can easily find features or make selections from an attribute table. You will now use this function to find out how many neighborhood parks are in this dataset. Open the Park attribute table. Open Select by Attribute dialogue box. You open the Select by Attribute dialogue box from the attribute table by clicking the Table Options button >Select by Attributes. Structure a query by choosing a field, operator and value. In the Select by Attribute dialog box, there is a SQL window where you structure your query by selecting a field, an operator and a value. In the Field: scroll down the list, double-click on the field: GEODB_SUBT and it appears in the SQL window. Then click equal operator button, and it also appears in the SQL window. Finally, click Get Unique Values and double click on Neighborhood Park and Click Apply. 13

14 Field Operator Value SQL Window Question: - How many neighborhood parks are in this dataset? - What is the total area of the neighborhood parks? 4.6. Field Calculator Using the field calculator, you can calculate values of a new field based on already available data. The exercise here is to add a new field to the attribute table of the Lake layer, name it area_hec and calculating the areas of the lakes in hectares using the field calculator. Tip: 1 square meter = Hectare 14

15 Right-click on the area-hec and click Field Calculator. You can type in the conversion formula (square meter to hectare) in the box provided in the field calculator using the information that is already available in the attribute table. Click Ok and the field will get populated with the areas in hectares. Your answers should look like the following: 5. Spatial Analysis in ArcMap: This section will provide an introduction to vector analysis, attribute handling, and the formulation of spatial queries Method: Let s imagine for environmental and habitat restoration purposes, the District of North Vancouver plans to relocate the bus stations that are within 50 meters of the creeks. Your first task will be to: Create a 50 meter buffer zone around the creeks; and Find out which bus stops are within that prohibited distance. 15

16 5.2. Buffer (Proximity Tool) Buffers are based on the concept of proximity. Buffers are created as polygons in a new layer. Turn off all the layers in your table of contents except for creeks, bus stops, and the aerial photo. On the menu bar, click Geoprocessing > Buffer. Next you will select the layer with the input features to be buffered, in this case Creeks. Create a 50 meter buffer around the creeks. The results should look like this: 16

17 5.3. Spatial Queries Spatial queries or selection of objects based on their spatial properties (i.e. placement) can be made using the Select by Location tool in ArcMap. The selection can also be based on a spatial relationship to objects in other layers. For example: Select all roads intersecting with a railway. Some of the available spatial queries ( Select by Location ) in ArcMap: Are crossed by the outline of This method selects the features that are overlapped by the features of another layer. For example, selecting wilderness areas crossed by the outline of roads will select any wilderness area with a road inside its boundaries. Intersect This is similar to the previous method, but it also selects any features bordered by the reference features. For example, selecting wilderness areas intersected by roads will select any wilderness area with a road running within its boundaries or alongside it. Are within a distance of This method selects features near or adjacent to features in the same layer or in a different layer. For example, if you have a layer of clean and polluted wells, you can find all the clean wells within 600 meters of the polluted ones. Or you could find the reservoirs and farms in other layers that are within 600 meters of the polluted wells. You can also use this option to find features adjacent to other features. For example, you may have already selected land parcels that your company might purchase, and now you want to get information about adjacent parcels. In this case, you would select the parcels within zero distance of the ones you ve already selected. Have their center in This method selects the polygon features in one layer that have their centroid in the polygon features of another layer. Are completely within This method selects features in one layer that fall completely inside the polygons of another. For example, you can select lakes completely within a forested area. To select features that are a distance from the edges of the polygon they fall inside, specify a buffer distance. For example, you can select lakes that are at least 600 meters within a forested area. Completely contain 17

18 You can select polygons in one layer that completely contain the features in another layer. For example, select forested areas that have lakes completely within them. To select polygons that completely contain features a certain distance within them, specify a buffer distance. For example, you can select forested areas with lakes at least 600 meters within them. Share a line segment with This method selects line and polygon features that share line segments with other features. You can t use this method to select point features. Touch the boundary of If you are selecting features using a layer containing lines, this method selects lines and polygons that share line segments, vertices or end-points (nodes) with the lines in the layer. The lines and polygons will not be selected if they cross the lines in the layer. If you are selecting features using a layer containing polygons, this method selects lines and polygons that share line segments or vertices with the polygon boundaries. The lines and polygons will not be selected if they cross the polygon boundaries. You can t use this method to select point features. Are identical to This method selects any feature having the same geometry as a feature of another layer. The feature types must be the same for example, you use polygons to select polygons, lines to select lines, and points to select points. Contain This method selects features in one layer that contain the features of another. This method differs from the Completely contain method in that the boundaries of the features can touch. For example, with the Contain method, a forest will contain a lake and thus be selected even if the border of the lake touches the border of the forest. The forest would not be selected using Completely contain because the borders touch. Are contained by This method selects features in one layer that are contained by the features in another. For example, you can select those cities that are contained by a county. This method differs from Are completely within in that the edges of the features can touch. 18

19 Your task here is to find those bus stations that are within the 200m buffer zone around the creeks. On the main menu bar go to Selection > Select By Location. Questions: - What is your Target Layer? - What is your Source Layer? - Which Spatial Selection Method has to be selected? - How many bus stops are located within 50 meters of creeks? Now it is time to export the results as a new shapefile. While the selected bus stops are still activated (shown by turquoise color), right-click on BusStop > Data > Export Data and export the selected features, give them a proper name, and save them in the same folder you keep all your other datasets. 6. Adding Essential Map Elements: Finally, there are a few elements that are considered fundamental to good map-making. While it is true that ALL maps do not need ALL of these elements (Does a map of the entire earth really need a north arrow?), it is also true that they can be critical tools in conveying spatial messages, when used properly. Here, we will take the final steps to complete our map layout, before exporting to portable formats. - Map Title: On the Main Menu, Go To Insert > Title. A window will pop up in which you can enter your map title. 19

20 2. You can then double-click on the title you made to change the size, font, etc. - North Arrow: On the Main Menu, Go To Insert > North Arrow. A window will pop up in which you can choose from a variety of north arrows. - Scale Bar: 1. On the Main Menu, Go To Insert > Scale Bar. Choose a scale bar from the list. When the scale bar is added to your map layout, Double-Click on it. A window will pop-up called Scale Line Properties. -Under Division Units change the units to Kilometers. -Click Apply and OK. You may drag the scale bar to make it bigger or smaller. - Legend: On the Main Menu, go to Insert > Legend. Select the layers you want to include in your legend from the Legend Items list and click Next four times and Finish the work. The Legend is added to the map. By now you should have a map with all elements. 20

21 6.1. Exporting Your Map 1. Save your Work. 2. On the Main Menu, go to File > Export Map 3. Click on the Desktop Button to browse to your working folder. 4. Change the Save as type to JPEG (*.jpg) 5. Change the Resolution to 300 dpi 6. Change the name of your map in File name: 7. Click Save. 8. Browse to the C:\Desktop\GIS-Workshop\ Folder and double click on the JPEG file you created from your map to view it in the default image viewer. 21