GIS Workbook #1. GIS Basics and the ArcGIS Environment. Helen Goodchild

Transcription

1 GIS Basics and the ArcGIS Environment Helen Goodchild

2 Overview of Geographic Information Systems Geographical Information Systems (GIS) are used to display, manipulate and analyse spatial data (data that contain a reference to a place). The great advantage of GIS over traditional cartography or Computer Aided Drawing (CAD) programs is in their ability to manipulate attribute information relating to the individual features in maps. They do this by working with several types of data. The following tutorial will introduce you to the GIS environment and prove step by step information on how to go about combining and analysing spatial data to make an archaeological map. Uses of GIS in archaeology (from Wheatley and Gillings 2003, 234) Many users of GIS are simply curatorial (e.g. making maps, visualising pre-existing information), but the system is far more powerful than this, with many spatial analytical tools to create new data. Spatial Analysis is one of the major applications of GIS with a long history in a number of disciplines, and the recognition of how people and resources are distributed in space has historically been applied to various fields and problems. 2

3 What can you do with ArcGIS? ArcGIS is used in many disciplines for a wide variety of applications, not just archaeology. We are, however, very adept at borrowing such approaches from other disciplines. Have a think about how these sorts of approaches might relate to archaeological landscapes. A tax assessor s office produces land use maps for appraisers and planners. An engineering dept monitors the condition of roads and bridges and produces planning maps for natural disasters. A water dept finds the valves to isolate a ruptured water main. A transit dept produces maps of bicycle paths for commuters. A police dept studies crime patterns to deploy its personnel and monitor the effectiveness of neighbourhood watch programs. A wastewater dept prioritizes areas for repairs after an earthquake. A telecommunications company studies the terrain to find locations for new mobile phone masts. A hydrologist monitors water quality to protect public health. A pipeline company finds the least-cost path for a new pipeline. A biologist studies the impact of construction plans on a watershed. An electric company models its circuits to minimize power loss and to plan the placement of new devices. A meteorologist issues warnings for counties in the path of a severe storm. A business evaluates locations for new retail outlets by considering nearby concentrations of customers. A police dispatcher finds the fastest route to an emergency. An emergency management agency plans relief facilities by modelling demand and accessibility. A water resource manager traces upstream to find the possible sources of a contaminant. A fire fighting team predicts the spread of a forest fire using terrain and weather data. 3

4 Data types Spatial data can be broken down into six basic themes: Points (e.g. settlements, find spots) Lines (boundaries) Areas (land use, soil types) Networks (roads, rivers) Surfaces (elevation, etc) Images (aerial photographs, satellite imagery) The two main data types which represent these themes are called raster and vector. Vector data is stored as co-ordinate pairs and represented as either points, lines or polygons, with associated attributes, often in tabular form. Raster data uses a regular grid-cell structure. The size of cells is on the basis of the data accuracy and the resolution needed by the user. The raster cell contains only a single discrete attribute value. Advantages Raster Defines geographical space simply Good at handling image and satellite data Good for continuous data with no definite boundaries (e.g. elevation) Good for map algebra Disadvantages Data intensive Larger file size Vector Good at working with clearly bounded features Good for network analysis Can link with databases Smaller file size More difficult to perform map algebra operations 4

5 Tables and relationships also play a key role in GIS data models, just as they do in traditional database applications. GIS organises geographic data into a series of thematic layers and tables. Since geographic datasets in a GIS are georeferenced, they have real-world locations and overlay one another The various components of ArGIS ArcMap. The main mapping environment used for all mapping and editing tasks as well as mapbased analysis. ArcToolbox. Where many functions are stored for data conversion and geoprocessing and spatial analysis ArcScene. An environment where you can display your data in 3D and is capable of moving a layer in space ArcCatalog. For managing spatial data and database designs, as well as recording viewing and managing metadata. ArcGlobe. Included with the 3D Analyst extension, this provides an interactive global view to work with geographic data. ArcReader. A free reader that can be used on any computer to view GIS projects but cannot produce or analyse data ArcGIS is highly customizable, and there are many other extensions available, subject to licence. 5

6 The ArcMap environment Extension Toolbars Table of Contents Map Frame Main tools When you open a new map you should find a left hand panel (named Table of contents ) which lists all the layers of your map and allows you to display and hide features. On the right is the map frame where spatial data is presented in map format. It is possible to view the table of contents in a number of ways using the tabs at the bottom left hand corner for drawing management, but we will look at this later. Along the top of the screen we have a familiar set of menu bars with various functions including SAVE etc. and down the right hand side tools for zooming, selecting, measuring, and querying are indicated by a series of button icons. ArcMap will not always look like this. The addition, movement and removal of toolbars means that you may have a different layout. You can customise the layout to your own preference. There are also two different views: Data View and Layout View. Data View is where you will work most frequently as Layout view is primarily for creating graphic outputs. 6

7 Creating, opening and saving projects To create a new project, select File > New. Select Blank Document > OK To create an existing project File > Open, navigate to the mxd file and click to open. To save a project go to File > Save. At this point it is also important to ensure you are in Data View by going to View > Data View. Adding, docking and removing toolbars To add new toolbars to the display, right click on an empty space on the toolbar area and select the item from the drop down list The toolbar will appear floating on the ArcMap screen. Docking new toolbars can be done by dragging it to the toolbar area. They can be moved by clicking and dragging the vertical line at the front of the toolbar To remove a toolbar, right click on an empty space to bring up the toolbar list, as above, and deselect the toolbar that you no longer require. Alternatively, go to Tools > Customize, or View > Toolbars. If an option is greyed out it may mean that the extension has not been activated, or we do not have a licence for it. To activate a licence go to Tool > Extensions to check/uncheck the ones you wish to load/unload. You will then need to load the toolbar in the usual way. EXERCISE 1.1 Load up ArcMap and create a new empty document. Ensure that the Editor, Spatial Analyst, Georeferencing and 3D Analyst toolbars are enabled and loaded, and that you are in Data View, then save your project. 7

8 Adding and Removing Data To add data to your project, left click the add data button, or go to File > Add Data. Navigate to the folder containing your data and click to Add. The file name will appear in the Table of Contents, and the data will be displayed in the Map Frame. If you can t see your folder, click the Connect to folder button to find your data Alternatively you can use the ArcCatalog tab, which will load on clicking the yellow icon Simply connect to your folder then drag and drop the files into your map window To remove data from a project, right click the file name in the Table of Contents and select remove. This will not delete the file. It simply removes it from the project. EXERCISE 1.2 Use the Add layer tool to add the following files from the TVP folder: av-dem toponyms allsites rivers roads landuse 8

9 Working with layers Layers can be turned on or off using the tick box next to the filename in the table of contents. The order of the layers in the TOC determines the drawing order in the map display, i.e. layers higher up in the table will be drawn above those lower down. They can be reordered by left clicking on the filename and dragging to the desired position. EXERCISE 1.3 Group the files into Geographic and Archaeological categories and order them as shown in the Figure to the right. Layers can also be renamed in the TOC this alters the display name but not the actual filename as stored on the computer. To do this, left click twice on the filename and enter a new name. Layers can also be grouped into convenient categories as a folder tree (cf My Computer). Simply select the layers to be grouped whilst holding down shift, then right click and select to Group. This can be renames in the same way as layers. Map navigation The Tools toolbar lets you move around the map and query the features on the map. Place your pointer over each icon (without clicking) to see a description of each tool. Zoom in/out (either a single click, or draw a box to zoom). Fixed zoom in/out Pan Zoom to full extent Go back to previous extent Go forward to next extent EXERCISE 1.4 Familiarise yourself with the navigation tools by exploring the map 9

10 Data paths and missing files Project files in ArcGIS have the file ending MXD. It is very important to remember that these files DO NOT CONTAIN YOUR DATA. They are simply a skeleton file which holds information about which files you have added, where they are stored, how you have ordered them, and how you have changed their appearance. Because the project stores data paths to the files you have used, it is very common when working on different computers to end up with broken links to your data. These show up as Red exclamation marks in your project. To re-connect with your data, simply click on the file, or right click and choose Data > Repair Data Source. You then navigate to the location of your file to re-establish the link. To avoid this in the first place, it is a good idea to set your data paths to relative. This means that, as long as you don t move around your folders, it doesn t matter which drive you use, as the project will only look for the folder structure rather than the drive letter. EXERCISE 1.5 Go to File > Map Document properties. At the bottom, check the box to Store relative path names to data sources. Click OK Save your project! 10