Via the Mapperz Blog, Nico Goeminne has created a reverse geocoder using the Google Maps API that brings up the closest street to a point of interest. Select a country/area that Google Maps supports geocoding for, zoom to the area in that country you’re interested in, and click on the map at your location of interest to create a marker. You’ll get the latitude/longitude of the point you clicked on, the name of the closest street, and the reference latitude/longitude for that street. A maximum of three markers on the map at one time, and a limit of 10,000 lookups a day if you use the source code for your own purposes.
For the US, more address-specific reverse geocoding is available at both the Reverse Geocoder for the United States and the Geonames Reverse Address Geocode.
Google Earth can display a scalebar in the lower left-hand corner of the display:
If you don’t see it, you can turn it on by selecting View => Scale Legend from the top menu. While it’s useful, it also has the drawback that it stays the same size on-screen as you zoom in and out, only the number above it that represents its length changing.
There’s a dynamically-sizable scalebar available as a network link from Safety Dave, available in two flavors (metric and English). Download the KMZ file, and open it in Google Earth; a colored bar will appear in the upper-left-hand corner, labeled with a specific distance:
As you zoom in, the bar will get longer and longer, until it fills the top edge of the display. Zoom in further, and it will shift automatically to a new scale 10x smaller than the previous one. For example, metric will go from 10 km to 1 km to 100 meters; English would go from 10 miles to 1 mile to 500 feet. The reverse will happen as you zoom out; zoom out too far, and the scalebar gets replaced by an error message.
You can always use the “Show Ruler” tool from the top toolbar to measure and display distances.
In a previous post, I described two basic online map projection viewers. Today, I’ll talk about another online map projection viewer that has far more capabilities than the first two, and is also a lot more fun to play with.
Continue reading ‘Online Map Projection Viewers II - A Great One From Brazil’
Prune is another Java-based GPS tool with its own unique set of features, including:
- Load multiple text, GPX or KML tracks, appending them to each other
- Trim duplicate points, and compress the track (hence the name Prune)
- Save combined tracks in text or KML format (use GPS TrackMaker to convert the KML tracks to GPX format if desired)
- See a plot of position, and altitude if available
Continue reading ‘Prune - Java-Based GPS Track Visualization And Photo GeoTagging’
Map projections can be defined as the science (and art) of depicting a curved surface as a flat one. You can’t depict the curved surface of the earth with complete accuracy on a flat surface like a paper map or computer screen, anymore than you can lay a flat sheet of paper on a globe smoothly without folding, wrinkling or tearing it. Transforming that curved surface to a flat representation requires mathematical manipulations of geometric parameters like scale, direction, and area, and that’s what map projections do. The type of map projection that’s right for your application will depend on what you want the map to show, the area it covers, and other factors.
Pictures of map projections are common in geography textbooks, and there’s even several books devoted to them, like Understanding Map Projections
and Flattening the Earth: Two Thousand Years of Map Projections. But there are also a number of online websites and stand-alone applications, that let you display, change and experiment with map projections, and this kind of interactive approach goes a long way towards making map projections understandable. I’ll be posting about a number of these websites and applications over the next week or so.
Continue reading ‘Online Map Projection Viewers I’
Two GIS programs I’ve posted about have recently released updated versions:
MapWindow: An updated version of Stable Release 4.4 is available. The only change I could spot is PostGIS import/export, but typically these updates include bug fixes as well.
SAGA: Updated to version 2.0.1. No huge changes, primarily fixes to the Linux GUI, a new tab that shows map thumbnails, and a few new modules.
The New York Times has an interesting article on the development of the new Clearview font that is likely to replace the old Highway Gothic font in US highway signage in the future. If you want to use the the Clearview font for map labels or signage, it’s available from this website, at a heavy cost ($795 for 1-5 workstations). But there’s an adaptation of the fonts available in TrueType format at the Roadgeek website that’s free for personal, hobby, educational or non-commercial uses (read the license on the website, and in the zip file, for the full details). Just unzip the fonts into the appropriate Fonts folder for your OS (for Windows, that’s the Windows\Fonts folder), and they should be available as a font selection in your application. Also included are versions of the old Highway Gothic font, as well as English and German highway signage fonts. And there’s a link to the Minnesota DNR’s TrueType font with recreational symbols.
The European Petroleum Survey Group (EPSG; now defunct, and superseded by the OGP Surveying and Positioning Committee) created and maintains a spatial reference database, assigning EPSG code numbers to spatial reference systems (combinations of coordinate systems, projections, and datums). There really is no way to figure out the spatial reference system from just the code number alone, or vice versa, so you need to look them up. The official database is in Microsoft Access format, not terribly easy to use; the code list in tabular format isn’t much better. There’s now a convenient online version of the database, searchable by keywords or code number. You can then access additional information for that spatial reference system in a number of different formats:
- Human-Readable OGC WKT
- Proj4
- OGC WKT
- JSON
- GML
- ESRI WKT
- USGS
- MapServer Mapfile
- PostGIS spatial_ref_sys INSERT statement
Users can also upload their own spatial reference definitions, which I suppose is a good thing as long as you exercise caution in using them.
Via import cartography.
