Web Viewers

Data Sources for USAGeneral Repositories:
  • DataBasin - Data Basin is a free, online system that connects users with spatial datasets, tools, and expertise. Individuals and organization can explore and download a vast library of datasets, upload their own data, create and publish analysis, utilize working groups, and produce customized maps that can be easily shared.
  • Earth Explorer - Generally just satellite imagery and aerial photography, but a good resource all the same.
  • ESRI ArcGIS Online Data
  • FSGeodata Clearing House - A source of raster and vector data focused on US Forest Service and Forestry lands in the US
  • GEON Portal
  • GeoCommunity Free Data Download - This is mainly US Data, and most is free...
  • National Atlas  - Raw data from the National Atlas is free to professionals for download. 
  • NPScape - NPScape is a landscape dynamics monitoring project that provides landscape-level data, tools, and evaluations for natural resource management and planning at local, regional, and national scales.
  • NRCS GIS and Data Sites - A comprehensive list of Web sites within the Natural Resources Conservation Service (NRCS) that are either GIS-related or contain data, documentation, or models that may be useful for GIS users.
  • USDA Geospatial Data Gateway
  • USGS Elevation Products
  • WEB-GIS Free distribution point for topographic and other data
LiDaR DataWMS - Web Mapping Services
Data by State &/or CountyIn the US, many States and Counties now have their own GIS Departments that make their data freely available on the web. This inlcudes LiDAR surveys! If you are doing work over there, just do a search for the local County Pages and have a dig around. Examples below:
Directory by State (hosted by University of Oregon)
IDAHO
  • ISU GIS Training and Research Center Geospatial Datasets
  • INSIDE Idaho (Interactive Numeric and Spatial Information Data Engine hosted by University of Idaho)
OREGONUTAHWASHINGTON

Data Sources for UK
  • EDINA Digimap
If you're at a subscribing UK University: most Ordinance Survey data is avaialble via Edina's Digimap If you were to download just a few of these layers from a commercial vendor, it would cost you 100's to 1000's of pounds. This is an incredible resource at your disposal. You can find all the OS Explorer, Land Ranger maps, national, regional, county and local boundaries, digital elevation data, historical maps, geological maps, and much more!
  • To use this resource, you need to login. If you are on campus (or using a VPN), this will automatically take you to your institution's login page. Off campus, you need to select alternative login, find your instiution, and then login.
  • Next, navigate to the Ordinance Survey Data Collections.
  • Inside, navigate to 'Data Download Services' and therein to Data Download.
  • From Data Download, select the data type you wish to use, and follow the wizard.
Where data is only available in a NTF format, you may find the following conversion tools helpful for converting NTFs into DXFs or MapInfo Files.
  • GoGeo - GI resource discovery site that has links to GI news, events, software and books as well as a metadata discovery portal that allows users to make geographical and temporally targeted searches for spatial data
  • ShareGeo  - ShareGeo is a repository for open spatial data. There are over 200 useful datasets that have been made available under an open licence for you to use. If you have any data that you would like to share, please contact the teamand they will upload the data for you.
Although the Ordinance Survey is one of the major sources of elevation data sets in the UK, you can not (that I'm aware of) download these datasets for free! They've sold the rights to do this to a host of private companies (e.g. GetMapping). Fortunately for you, as long is you are at an academic institution (UK only) you can download much of the data for free from EDINA . 
Landmap provide a 30 m raster DEM for the whole of the UK (derived from Multiple passes of an ERS SAR sensor). You can download the data in 100 km tiles, or by defining your own boundaries. This resource is free to UWA students and staff.
The NERC Earth Observation Data Centre (NEODC) is a Designated Data Centre of the Natural Environment Research Council (NERC) and as such it is tasked with the acquisition, archiving and provision of access to remotely sensed data of the surface of the Earth acquired by satellite and airborne sensors.
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