Exploring the world of free tools for GIS, GPS, Google Earth, neogeography, and more.
In earlier posts on MicroDEM, the digital elevation model (DEM) has been displayed in reflectance mode, terrain illuminated by light coming from an angle. But it’s also possible to display the elevations as different colors for use as a background image for maps, or for shading.
Continue reading ‘Elevation And Contour Line Display In MicroDEM – Make Your Own Simple Topo Maps’
There’s a new service from the USGS that lets you download 1:24K, 1:100K and 1:250K topo maps for anywhere in the US in GeoPDF format. It has an easy-to-use interface based on Google Maps that makes finding your location, and downloading the desired maps in compressed zip format, straightforward.
Continue reading ‘Downloading USGS Topo Maps In GeoPDF Format, And The GeoPDF Plug-In’
In addition to the standard image overlays of Map, Satellite and Hybrid for Google Maps, the Active Trails website has an additional overlay button – Topo, for topographic maps. At lower zoom levels, the 1:100K scale USGS topo maps are visible, but if you zoom in close enough, the larger-scale 1:24K maps become visible. Comparing Map, Satellite and Topo overlays, there appears to be a good position match between the three. Active Trails also has placemarks for many kinds of outdoor trails across the country (hiking, biking, equestrian, etc.) entered by site users. You can also install a network link in Google Earth that will let you view the trails there, similar in nature to the new Google Earth layer from Trimble.
Addendum: Fixed the Active Trails links (sorry about that). In the comments, MH points out the ACME Mapper 2.0 site, which is a better choice. It displays black-and-white USGS aerial photos, and also lets you print out a copy of the on-screen map with the push of a button.
The Map Room posts on GeoGratis, the Canadian Government’s new web gateway for free geographic data, both raster (topo maps, satellite images, etc.) and vector (hypsographic, political, etc.). No DEM (digital elevation model here), but you can get 90-meter data for Canada from the Geobase website or the USGS Seamless Server.
Doc Savage’s Old Word Archaeology website (great name!) has links to maps aerial/satellite photos, and vector data for most of Israel and Jordan, with some data for surrounding areas (mainly Syria and the Sinai); click on the links under “Digital Data” on the right. Most of the data is georeferenced for direct use in GIS software. Data includes:
The Relief Shading website defines “shaded relief” as “a method for representing topography on maps in a natural, aesthetic, and intuitive manner”. A review of the many resources on that site, and on Tom Patterson’s excellent Shaded Relief website, will convince you quickly that getting the best possible results requires a great deal of knowledge, expertise and time. But you can get fairly satisfactory relief shading of your maps quickly and easily using 3DEM.
1/12/2010: Unfortunately, the latest versions of the TatukGIS viewer have removed the “Export To Image” function, which was the most valuable function of this program. So I can’t really recommend it anymore; you’d be better off with a free GIS program like qGIS, MapWindow or MicroDEM, which do offer raster combination and export functions, albeit without the same degree of control as the older version of TatukGIS Viewer. If you look around online, you might still be able to find the older version somewhere.
The USGS Seamless Server data gateway I posted about yesterday has a filesize limit per download of 250 MB uncompressed (the zipped, compressed size of the downloaded files is usually much smaller than the uncompressed size). If raster map data you’ve selected for download has a combined size greater than 250 MB, the server breaks it up into smaller segments, each downloadable as a file. If you import all of these separate files together into a GIS program, it will automatically position all the pieces together in the right place. But you might find it more convenient to combine all of the individual pieces together into a single map file with the same resolution, and still georeferenced.
Over the next few weeks/months, I’ll be putting up a fair number of posts on software tools that work with Digital Elevation Models, or DEMs for short. A DEM is essentially a grid of an area where each point in the grid represents the elevation or altitude at that point. With a DEM, you can do things like determine the altitude and slope at a point, measure the terrain profile, make 3D views (both static and interactive), and so on. Before starting those posts, it makes sense to talk about a good source for that data.
Continue reading ‘The USGS Seamless Data Distribution System’