Intro to Open Source GIS Software QGIS
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This document provides an introduction to GIS and QGIS. It discusses: - Who the instructor is and their background in GIS. - An overview of what GIS is, including its ability to store, manipulate and display geographic data, and how it can be used to analyze spatial relationships and patterns. - A brief demonstration of QGIS and its capabilities. QGIS is an open source GIS software that can perform many of the same functions as ArcGIS desktop.
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Intro to Open Source GIS Software QGIS
- 1. Intro to GIS/QGIS Erich Purpur epurpur@virginia.edu 434 924 1557
- 2. Who am I? Erich Purpur Research Librarian for Science & Engineering Brown Science & Engineering Library -Serve as Liaison to various engineering departments at UVA -Help people with research -information discovery -python programming -GIS projects -Teaching -For-credit classes and workshops -both GIS and python
- 3. GIS Experience -BS in Geography w/ GIS concentration -Worked on wetlands ecology protection projects -started offering GIS services (similar to Scholar’s Lab) at previous job -Now: -teach GIS related classes and workshops -sometimes help people with research projects -GIS consulting on the side -All QGIS all the time -and other open source tools (python, PostgreSQL)
- 4. What will you learn today? -Familiarity with GIS concepts -Talk about project workflow -Self Help
- 5. Shortcomings of this workshop -Limited Time -Not Specific to your needs
- 6. What is QGIS? -Free and Open Source GIS Software -An OSGeo project -packaged with a bunch of other open source libraries and tools -An alternative to ESRI/ArcGIS
- 7. Why use QGIS? -Because it is free -Linux and Mac compatible -Because you are a fan of open source / are a developer -Maybe you are an ESRI hater?
- 8. What can you do with it? -Pretty much everything you can do with ArcMap, ArcGIS Pro, or ArcGIS online -different functionality available as well, because people build their own -same file types as ArcGIS, import between them
- 9. Traffic Map Flight Tracking Map Bus Routes How are you using maps today?
- 10. What is GIS? -A computer system capable of assembling, storing, manipulating, analyzing, and displaying geographically referenced information. What does this mean? -GIS is a data visualization tool and is useful for looking at spatial relationships and patterns between objects. You can discover and communicate meaningful patterns in your data -GIS is not scary and is not only for geographers. A GIS is a tool which applies to nearly every field including the sciences, humanities, social sciences. -The output is a map but the power lies in the data behind the image -GIS skills are a literacy
- 11. What does it look like?
- 12. What can you do with GIS? -Show where things are -Show change over time/track changing data -See and communicate meaningful patterns in your data
- 13. Properties of Real World Geographic Information -Location -Attributes -Spatial Relationships
- 14. Geographic Reality -Geographic features are recreated on the computer using Data Models Vector Data -Point, Line, Area (polygon) -Values can be assigned to each point, line, or area Raster Data -breaks the earth down into a grid -each cell represents an area in real life -Spatial resolution -values are assigned to each grid cell, much like values are assigned to each vector point -common examples: -Satellite images
- 15. Spatial Resolution Low Resolution = large area High Resolution = small area
- 16. Location of Objects -the absolute location of objects is determined by coordinate systems Geographic Coordinate System -a network of intersecting lines -latitude (North/South) -longitude (East/West) -starting point at the intersection of equator and prime meridian
- 17. Map Projections -Because the earth is round, displaying it on a flat surface is problematic -The image will be somewhat skewed -Different projections focus on different areas of the earth and attempt to eliminate skew -Getting data to display in the same map projection is sometimes easier said than done.
- 19. Attributes -Unlimited amount of attributes can be assigned to an object -stored in an attribute table
- 20. GIS Projects… Gathering Data -often times the hardest part! -Data can be found… -online data repositories (add more info and images) -City of Charlottesville has a data portal -remote sensing -taken by satellites in space -Digitizing/Scanning paper objects -gather it yourself -with a GPS unit -sometimes it appears via some form of luck and magic Data Storage -occasionally massive amounts of data are used and storage can be an issue
- 21. Self Help! -There are a lot of resources and a huge user community online -Your question is not unique -QGIS Documentation - https://www.qgis.org/en/docs/index.html -ArcGIS Documentation - https://doc.arcgis.com/en/ -Stack Exchange – An entire GIS and QGIS arm - https://gis.stackexchange.com/ -GeoNet – ESRI’s Online Community - https://community.esri.com/
- 22. How to learn more QGIS -Follow up with my workbook -Learning QGIS 3rd Edition – Anita Graser https://search.lib.virginia.edu/catalog/u7237739 -available through UVA library! -Ask for more help -me or Scholar’s lab
Hinweis der Redaktion
- Hi Everyone, my name is Erich Purpur. I am a librarian in the DeLaMare Science & Engineering Library. The DeLaMare library exists on campus for everyone, but specifically we serve the needs of the science and engineering community on campus. I have a BS in Geography with a GIS concentration from Appalachian State University, and a MS in Library Science from the University of North Carolina, Chapel Hill. Though my background is in GIS (Geographic Information Systems) I have several job responsibilities, which are: 1- The DeLaMare Library hosts a makerspace, much of which is on the first floor. We provide access for all to expensive/rare tools and equipment like 3D printers, 3D scanners, laser cutter, vinyl cutter, lendable technology, collaborative learning space, and more. The care, feeding, maintenance, and upkeep of these resources is a shared responsibility among DeLaMare staff. Our technology is available for anyone, including people unaffiliated with UNR. Learn more about our resources here: (http://www.delamare.unr.edu) 2- I am a liaison to several departments on campus. Which means, if they need something from the library to support their curriculum and research, I am the official library person they are supposed to go through to acquire this. My current liaison responsibilities are Geography, Civil & Environmental Engineering, and Biomedical & Electrical Engineering 3- GIS! I coordinate GIS services at UNR libraries, which are primarily hosted in the DeLaMare Library. We offer walk-in tutoring availability Monday-Friday for anyone. Hours vary by semester, but tutoring generally happens in the afternoon. See tutoring availability here: (http://unr.libcal.com/booking/GIS). I am also happy to meet at other times if those don’t work for you. In addition, I teach this exact Introduction to GIS class the first Friday of each month at 2pm in room 121 in the Knowledge Center, also called the Dataworks Lab.
- This is sort of a nuts and bolts introduction to GIS and its applications. Today I hope to familiarize you with GIS concepts such as data models and map projections. We are going to walk through a simple exercise using ArcGIS which I hope serves as an introduction to the software. Things I hope you gather from the exercise are: -Most people only need a small subset of GIS functionality available in the ArcGIS software package. -Depending on your needs, you may not need to learn ArcGIS. You could use ArcGIS Online, Google Earth, or another free mapping tool. Many tools exist and finding one to meet your needs is important
- Map literacy skills are important and you already have them because you use them in your every day life. Take a look the 3 common examples of map usage.
- The plain old definition of “What is a GIS?” never really resonated with me. Seeing the definition actually put into play was a lot more valuable I feel like. But we will get there later. A GIS is basically a tool for data visualization, which can be applied to nearly everyone’s work and research including people in the sciences, humanities, and social sciences. Geographic Information Systems model real world objects by representing reality through data models. Attributes are linked to these objects to make them more meaningful. Finally, the spatial relationships between objects are examined to determine value and patterns in whatever it is you are studying. You do not need to use ArcMap to do this. Tools like Google Earth can be useful too. Depending on the project, you may be able to get away with using Google Earth to show relative locations of things. Simple data layers like roads and points of interest are built into Google Earth and you can add your own information to Google Earth maps too. Lastly, GIS skills are a literacy just like any other software program, learning to manage your money, playing an instrument, etc. They can be learned but there is a learning curve.
- All the layers are stacked on top of each other to create a representation of the real world. Just like layers in a cake, only the top layer is visible.
- The most common things people use GIS for are not overly complicated. Once again, GIS is a data visualization tool which you can use to see patterns and trends in spatial data. Figuring out the spatial relationships between objects has a lot of value in nearly every field in some way or another. Common things people use GIS for: -Show where things are -Show change over time -keep track of changing data -communicate meaningful patterns in your data Really, the last bullet point is the most important, and the point of all of this. The end results of most GIS projects is a map. Your map should be readable to key stakeholders, who often don’t know much about your project. If you communicate the meaningful patterns in your data, you can get the point across to others.
- I like to use this map as an example of what data can be communicated visually. Take this map of Los Angeles county schools. The black shapes outline school districts. Each school district is shaded based on the average income of that area. On top of that, we have yellow and red dots. Red dots indicate areas where more than 30% of schoolteachers are uncredentialed. Yellow dots indicate areas with fewer than 10% uncredentialed teachers. Now, lets think about what these colors and dots mean. The shading tells us not only about income, but other demographics of this area. In LA county, like most places, wealthy people live near each other and poor people live near each other. In this case, rich people live in the hills surrounding the city, while poor people live in the valley. This also probably tells you something about the spatial distribution of ethnicity as well. Regarding the dots, red dots are “warning” signs and are clustered in areas of low income. Yellow dots are in areas of high income. Obviously, rich people have more money to pay for good teachers. However, sometimes when viewed spatially, you can see patterns in your data that were not previously obvious when viewed in a tabular or some other format. This can steer your decision making in the future.
- As we saw in slide 7 (“What does it look like?”), every facet of the real world is represented as a layer, but not all layers are equal. What is geographic reality? A computer creates a representation of the earth by using data models. A data model is a method used to represent real world objects on a computer. There are basically two data models used in a GIS, vector and raster. Vector Data- Represents real world objects as points, lines, or polygons. This is used for representing clearly defined objects on the landscape like trees, houses, roads, etc. It is also useful for defining spatial relationships. You can see that a river flows into a lake or that trees are north of the river. Raster Data- breaks the earth down into a grid where each cell represents an area in real life. The amount of area represented by each cell is known as the spatial resolution. Values are assigned to each grid cell, much like values can be assigned to a vector point. The value assigned to each grid cell is the average elevation, land cover, etc value across that grid cell. Common uses: Satellite Images, DEMs Raster data is used for representing continuously changing attributes over space
- Here same image shown with different spatial resolutions. The optimal spatial resolution is determined by the size and scope of your project. High resolution is good but also leads to large files and slow processing time. If you are studying the entire United States, you probably don’t need 1meter spatial resolution but if you are focused on a town or neighborhood, small resolution will be more appropriate. Low resolution imagery isn’t necessarily bad. The optimal resolution just depends on the study area of your project.
- The absolute location of objects on the earths surface are determined by coordinate systems. Geographic Coordinate Systems are a reference system for the curved surface of the earth. These lines of latitude and longitude determine the absolute location of objects on the globe. For example, Reno’s latitude/longitude is about 39.53 degrees North, 119.82 degrees west. This will be written as 39.53, -119.82. Why -119.82? This is because the earth is divided into 4 quadrants, known as hemispheres (north, south, east, west) with the nexus being at the intersection of the Equator and Prime Meridian. This point lies in the Atlantic Ocean off the coast of Africa. Latitudes north of the equator are positive, south of the equator are negative. Longitudes east of the prime meridian are positive, west are negative. This is why Reno is at -119 degrees west. Be careful here, if you list Reno’s latitude/longitude at 39.53, 119.82, your point will be located somewhere in North Korea.
- The age old question geographers have faced is: how to display a round object (the earth) on a flat surface? The answer is Map Skew. Because the earth is round, displaying it on a flat surface is problematic and the result of this will be a skewed image. Take the above image as an example. This is a screenshot from Google earth of the entire world. You can’t see lines of latitude, but they are spaced further apart as you go north or south from the equator, creating skew. In this map, Greenland looks to be about the size of the continent of Africa. In reality, Greenland is about ¼ the size of Africa. More about this later… The solution to map skew are map projections. Different map projections focus on different areas of the earth and attempt to represent these features accurately, thus eliminating skew. Many map projections exist including ones focused on the western hemisphere, north America, Nevada, Nevada West, and so on. A note about map projections in ArcGIS: Getting data to display in the same map projection is sometimes easier said than done. Quite commonly, you gather data from different sources. This data will be in different map projections and when imported into your map document, it won’t line up where is should be in the rest of the data. Fear not, this is a fixable problem. The issue is probably that your new data is projected differently from the existing data in your map document.
- As I was saying, you are probably looking at skewed maps without even knowing it. Take a look at this website (www.thetruesize.com) and play with it. Type a county or state into the search box and then drag it north or south of the equator to see how big it really is. Take the Greenland example from the previous slide. Choose Greenland as your country, then drag it to overlay with Africa. Here you will see the true size of Greenland compared to Africa.
- You have objects represented as layers on your map. But the real power in your objects lies in the data associated with those objects. These are stored in the attribute table. Just like a spreadsheet, data is organized into rows and columns. An attribute table can have thousands of rows and columns. I assume this is a limit, but I have never reached it. As you can see in the above example, there are 7 objects represented as points. The attribute table is shown which contains various data fields (columns) for each object. You can use the data in the layer’s attribute table to manipulate it, pair it down, expand upon, etc.
- Just like any project, GIS projects follow a workflow. Once you have decided what it is you want to analyze, you must gather the available data. Often times this is the most difficult or most time consuming part of the project! The analysis is the easy part (or usually less time consuming). Data can be gathered from various sources which usually needs massaging and editing to get everything to line up in the same format. Today, online data repositories, often provided by government agencies provide data. This is often municipal data such as census tracts, public utilities, or aerial imagery. Or maybe your agency already has previously used datasets ready to go? Remote sensing data is available online, which is are usually satellite images taken from space. Sometimes historic maps or documents can be digitized or scanned to reveal information. Often times data has to be gathered yourself. I have done this by hand with a GPS unit, taking coordinates and later adding these into ArcMap. Other times, the data is out there but is sitting on someone’s hard drive or server. Sometimes you get hint of this data via word of mouth or sometimes by asking contact people the data you need might surface. This method is hit or miss at best.