For a long while the most frequent question I got from other GIS users was, "hey, can I have a copy of your county map shapefile?" This really easy to get from the Ohio Transportation Mapping System website, but somehow I still end up emailing out this file at least every couple months. Today I'm… Continue reading Data Downloads: State and County Maps
Today I'm continuing a series on sources of spatial data (see past posts on aerial images and DEMs). Soil maps are useful for all sorts of applications, like deciding where to place a trial in a larger field so that all the treatments are on the same soil type or determining the drainage class of… Continue reading Data Downloads: Soil Maps
There are four types of spatial data I download frequently for research purposes-- aerial images, digital elevation models (DEMs), soil maps, and county or other political maps. You can learn more about the first type, aerial images, in one of my early blog posts about Google Satellite, OpenLayers for QGIS, and OGRIP. Today I'm going… Continue reading Data Downloads: DEMs
Are you as obsessed with ColorBrewer as I am? I am making a map where I color Ohio counties based on region, and used ColorBrewer to pick colors. The first thing I did was go to ColorBrewer and find a qualitative color set for 5 categories of data. Next I used the HEX codes provided… Continue reading Getting Category Colors into QGIS from ColorBrewer
If you missed my posts on terrain derivatives or SAGA, you may want to jump back and read those first. Today I'm going to talk about two very common terrain derivatives and how to calculate them in SAGA. I'm going to keep going with the same DEM from Mt. Gilead State Park I used in… Continue reading Basic Terrain Analysis: SAGA
Last week I mentioned terrain derivatives and promised some how-to posts. I'm going to start with an brief intro to SAGA GIS, which is my preferred software for generating terrain derivatives. SAGA was written in the early 2000s and has been regularly updated-- you can learn more from its makers here. You can download SAGA… Continue reading Intro to SAGA GIS
Lots of people have been asking me about terrain derivatives lately, and I've been putting off blogging about them for a while because I just didn't know where to start. Instead of one master post with all the things I decided to split it into some more manageable chunks-- for both your sake and mine.… Continue reading What are terrain derivatives?
Over the last month or so I've had a little series about how we describe positions on the globe and how we visualize spherical space on a 2D map. I started with big picture information, like why we care about map projections. Last week began giving more concrete advice for picking a projected or unprojected… Continue reading EPSG Numbers and Coordinate Reference Systems
More map making! When you're first starting a new project and have data files in different projections, you can still view all your data together at once, using something called on-the-fly projection (a common feature of most GIS software). On-the-fly projection displays all your files using your "project CRS" and lets you have map layers… Continue reading Selecting a Projection for Spatial Analysis
Shapefiles are one of the main types of data you work with in a GIS. I have a description of GIS here, and an intro to the other basic data type (rasters) here. Shapefiles are vector data, and vector data comes in three basic forms: polygons, lines, or points. Polygons are shapes that take up… Continue reading What is a Shapefile?