Hi Tony, Below is a link to the slides I use for our Intro to GIS workshops. I need to update it to match my own internal script which differs a little from what's in the notes. But I've found the graphics I use on the 1st slide for coordinate systems to be very helpful in explaining this to new students. The key concepts are: * Coordinate systems (spatial reference systems) describe the virtual model* of the earth in a GIS and are how we pic or represent our data on the model. *the model reference links back to slide 5 where I describe the Key Characteristics if a GIS. * Coordinate systems are composed of 2 main parts: 1) the datum, which is the mathematical model representing the shape and size of the earth and 2) a coordinate system, which links our data to that model. * I start with Datums, explaining the differences between concepts of the earth as sphere, ellipsoid, and its true shape. Talk about how the ellipsoid is a middle ground that best represents the earth without the extra complexity of a true shape model. The talk about how that ellipsoid is positioned in different ways to model global vs local systems. * Next is coordinate systems "if the datum is the model the earth, the coordinate system is how we pin data to it... just like Datums can be local or global, coordinate systems have two main types, Geographic and Projected..." This is where things get dicey! I try my best to explain what a geographic system is vs a projected one and why it matters in a GIS, mostly demonstrating how the measure of distance for longitude changes as we go up/down in latitude but the value of the long does not. e.g "1* long at the equator is 111km, halfway up the globe it's about 78km, and at the pole its 0km... but it's always 1* of longitude, that means we can't use a geographic system for the most important aspects of a GIS, measuring distance and area between features". * I don't dwell on types of projections that much but describe the 4 projection characteristics and how they change w dif projections. * I do not talk about transformations! Way to technical for most new users. I leave students with these core concepts: Coordinate systems determine the virtual model of the GIS and how our data is displayed on the map; most raw data is geographic, we usually need to change that to projected for analysis; the choices we make in what new coordinate systems to use affect the envelope for that systems accuracy (global/local) and the function of the system related to things like preservation of Area/Dist etc... * I always tell them not to worry too much about all of this right now, but to keep in mind what a ref system is and that when they start any new project its best to come talk to someone like me for specific help in determining what steps to take next. * The hands on lab reinforces all of this by demonstrating mismatches between data and GIS project coordinate systems, where to look up the system of ea layer or the project, and how to change the project to match the data 9we leave re projecting data off the intro workshop). This is all very hard to describe in text so if you have any other questions I'm happy to talk more via Zoom! https://docs.google.com/presentation/d/18idr6owlqYo4UmrE-h2F6_J_AP1QB9MoDGCSgvscuaM/edit?usp=sharing [https://lh5.googleusercontent.com/e2KBu2opQWzqSqv63VQxRgPgqr7LyUVAZPimusXY8cfsA-m-aCUWbUu5IK3oiCDuPBrcG-3eAdY1yg=w1200-h630-p]<https://docs.google.com/presentation/d/18idr6owlqYo4UmrE-h2F6_J_AP1QB9MoDGCSgvscuaM/edit?usp=sharing> Intro to GIS<https://docs.google.com/presentation/d/18idr6owlqYo4UmrE-h2F6_J_AP1QB9MoDGCSgvscuaM/edit?usp=sharing> log in and welcome Intro to GIS workshop - 3 hours w discussion Part of a series on GIS use (sign up for email list) Starting point to working 1:1 in GIS lab Credits: http://www.statsmapsnpix.com/2016/10/the-global-human-settlement-layer.html https://www.washingtonpost.com/graphics/2017/national/... docs.google.com David Medeiros Geospatial Reference & Instruction Specialist Stanford Geospatial Center 650.561.5294 @mapbliss SGC website: gis.stanford.edu GIS cartography: bit.ly/giscart<http://bit.ly/giscart><http://bit.ly/giscart> GIS email list: bit.ly/GISlist ________________________________ From: Maps-L: Map Librarians, etc. <[log in to unmask]> on behalf of Diaz, Tony A. <[log in to unmask]> Sent: Thursday, May 19, 2022 7:31 AM To: [log in to unmask] <[log in to unmask]> Subject: QGIS, question about projection transformation screen Hi folks, I’m going to start teaching an introduction to QGIS class later this year, for newly arriving students here at my institute. Would anyone have an easy explanation I can say about projection transformations? I have an idea of what it is, but I was hoping if someone could chime in on a simple explanation for someone new to GIS to understand what this means when a user comes across it. Also, what transformation would one use and why? (Example, in the attached screenshot, which of these would I choose and why). Thanks again, Tony Diaz California Institute of Technology Pasadena, CA