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
Before I get off the datum topic, I want to share a little bit about what datum the National Geodetic Survey (NGS) is moving towards. The NGS is a part of NOAA, the National Oceanic and Atmospheric association. If you use weather.gov for anything, you're familiar with the outputs from NOAA. The current official datums… Continue reading New Datum for North America
Earlier in the week I gave a quick overview of map projections. Today I'm covering a related topic--datums. North American Datum 1983 is the basis for a lot of common map projections, and World Geodetic System 1984 is the series of latitude and longitude most commonly used on consumer GPS devices. But first, what's a… Continue reading What’s a datum?
At the most basic level, map projections are how we turn the 3D earth surface into something flat. There are polar projections that look at the globe from the top or bottom view, or more common projections that are centered near the equator. Map projections are really easy to overlook, but have large impacts on… Continue reading What’s a map projection?
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?
I'm taking a quick break for data collection tools to share a feature of Google Maps I use all the time-- bike routes! I love my bikes almost as much as I love my dogs.... I bike for transportation more days than not and am pretty familiar with the trails and bike-friendly roads in my… Continue reading Bike Routes!