Tuesday, January 27, 2009

AfricaMap beta now available - new online GIS site

The beta platform of Harvard Center for Geographic Analysis launched AfricaMap

It is a free website that brings together a huge amount of geodata on Africa. Long awaited its now publicly available. It includes a lot of data layers and is a good beginning for bringing together the available data sets of Africa.

  • Complete Soviet topographic maps at 1:500,000
  • Satellite imagery
  • Soil data
  • Ethnographic regions
  • Languages
  • HRAF + ethnologue
  • 1:2,000,000 surficial geology layer
  • 1,000,000 placenames from Geonames

Additionally many historic maps have been scanned and geo-referenced to

overlay such as the data from the Harvard Museum of Comparative Zoology,

Transatlantic Slave Trade database and A lot more!!!

Metadata is attached to vector rectangles of individual

map sheets, which all have been de-collared.

Anything not protected by Crown Copyright (or other copyright) will be available for download.

It also includes JING application which is a great app for extracting

selections from the map and exporting them to include in a publication

if you credit and cite properly.

So browse at http://africamap.harvard.edu

Some part of the data is still in the test mode (in the servers )although majority of it is

in the public website right now. It runs best on Firefox 2.0, but also runs fairly well on Internet Explorer 7.0

Thursday, January 15, 2009

Easy Elevation Download - CGIAR-CSI

Here is something to elevate your GIS spirits. CGIAR Consortium for Spatial Information have a established a user friendly option to download SRTM elevation data which is originally produced by NASA. There is now a simple and fast way to download the SRTM tiles. Click here to access the download page. As you can see in the image above, I want to download all tiles for Indonesia. I have selected the tiles I need for this and then clicked the click here to begin search button. You will get a list of all the tiles you have selected and you can download them easily by clicking on the data download arrow.

The SRTM 90m DEM's have a resolution of 90m at the equator, and are provided in mosaiced 5 deg x 5 deg tiles for easy download and use.

Newbies: For all you newbies who are looking for contour lines, you can use these images to create them. Download the open source software MapWindow GIS. Open MapWindow GIS and click on Plugins > GIS Tools. Click on GIS Tools in the top menu and then go to raster> generate a contour Shapefile. Then specify the contour interval and directory and click Generate.

Tuesday, January 6, 2009

Image Data - for Pro's and Newbies

If you are looking for some nice satellite images, the USGS Global Visualization Viewer is the tool for you. Once you scroll to the image you need, right click and choose "add to list". On the bottom left hand side, click the Download button to retrieve the image. Note that most images are downloadable but some are not. Tweak the date in the of the image to find a downloadable file.
can also choose the collection of images on the top "Collection" menu. The Landsat Archive - "L7SLC off (2003+)" are your best choice for up to date images. However, they have some annoying lines running through them, but still they are useful for a lot of scientific work. If you just need a nice backdrop image choose Landsat Decadal and "ETM+ Pan (1999-2003)". All images have a resolution of 30m or 15m (per pixel) if pan sharpened. For a groovy display of recent or temporal data use the L7SLC images and digitize interesting features as Shapefiles, then display them on the older ETM+Pan backdrop image.

If you are working in a country with a bad internet connection make sure you install a download manager before you start the download. This will help as it resumes downloads even if the connection has been interrupted or the computer has been shutdown.
The images are zipped and around 250mb. Unzipped, they will be around 1GB. Since you will get all image bands, use the open source software OS
SIM for stacking and pan sharpening your images. Here is the link to the PDF Tutorial for the easy to use and stable software.

To unzip the images you will need to use IZArc as Winzip will not do the trick.

If this stuff bores you and you want to explore other remote sensing data options such as radar etc. use NASA's EOS Data Gateway.

If you are a GIS newbie and don't k
now about bands and all that fun stuff, you can download pretty good images (250m resolution) from the True Marble website.

A good alternative is also to embed Google Earth images into your GIS software. Download MapWindow GIS (easy to use and stable open source GIS application) along with the Google Earth plugin. After installation, open Google Earth and navigate to the image extent you need. In the MWG Plugin Menu, select Shape2Earth. The Shape2Earth menu will appear. Here, click on "Get image from GE" and save the image to your computer. It will be georeferenced. If you need the image in color use these instructions.

If the term GIS scares you and you just want to look at an image, use Google Maps or Google Earth. Or try FlashEarth which will also show you images of other digital globe applications.

For all users with a bad internet connection try saving the Google Earth images to your hard drive by caching them. This means you can view the images using Google Earth even though you are not online. It is quite easy to do. when you have internet connection, open GE and zoom to the image you would like to save. That's it! Now go offline and you will see that this image is saved when you open Google Earth and navigate back to the previous extent.