Archive

Posts Tagged ‘land use’

Historical Imagery for the entire world now available via Wayback Service in ArcGIS from Esri

I know that many of you regularly want to examine changes-over-space-and-time with imagery and GIS for research or instruction purposes.   As of last week, 81 different dates of historical imagery for the past 5 years now reside in ArcGIS via the World Imagery Wayback service.   For more information, see: https://www.esri.com/arcgis-blog/products/arcgis-living-atlas/imagery/wayback-81-flavors-of-world-imagery/

You can access this imagery in ArcGIS Online, ArcMap, and ArcGIS Pro.  A great place to start is the World Imagery Wayback app – just by using a web browser  – https://livingatlas.arcgis.com/wayback/    A fascinating and an incredible resource for examining land use and land cover change, changes in water levels of reservoirs, coastal erosion, deforestation, regrowth, urbanization, and much more.  This resource covers the entire globe.

However, in keeping with the theme of our book The GIS Guide to Public Domain Data and this blog of being critical of the data, caution is needed.  The dates represent the update of the Esri World Imagery service.  This service is fed by multiple sources, private and public, from local and global sources.  Thus, the date does not mean that every location that you examine on the image is current as of that date.  I verified this in several locations where my ground observations in my local area show construction as of June 2018, for example, but that construction does not appear on the image.  In addition, several other places I examined from wintertime in the Northern Hemisphere were clearly “leaf-on” and taken during the summer before, or even from the summer before that.  Therefore, as always, know what you are working with.  Despite these cautions, the imagery still represents an amazing and useful resource.

wayback1wayback2

Sample from this imagery set for 30 July 2014 (top) and four years later, 27 June 2018 (bottom) for an area outside Denver, Colorado USA. 

Advertisements

VGI Data Sources: Assessing Completeness and Correctness

November 2, 2015 3 comments

In a recent article published in the ISPRS International Journal of Geo-Information, Quality Evaluation of VGI Using Authoritative Data—A Comparison with Land Use Data in Southern Germany, the authors investigated some of the concerns regarding data quality and data usability often levelled at Volunteered Geographic Information (VGI) data sources.

The objective of the study, based in the Rhine-Neckar region of southern Germany, was to compare OSM data to the authoritative land use and land cover (LULC) data set ATKIS Base DLM version 6.0. published by the LGL mapping agency (Baden-Württemberg State Office for Geoinformation and State development).

The results for the OSM data completeness and correctness comparison were variable across the different classes of land use in the study area. However some general trends emerged including:

  • Areas with a high percentage of forest cover were the areas with the highest level of completeness and correctness.
  • Other classes (incl. farmland and urban areas) had low levels of completeness but higher levels of correctness; features present were mapped accurately but some features were missing.
  • Other areas (incl. quarry and lakes) had high levels of completeness (most features mapped) but had a greater percentage of incorrectly mapped features.
  • There was a marked difference between rural and urban areas; the study identified higher OSM coverage and thematic accuracy in densely populated areas (more people available/interested in collecting the data?).
  • Some land use classes demonstrated both high levels of completeness and correctness, suggesting they had been mapped for a specific purpose.

Although not intended as a definitive statement of OSM data quality, the study suggested that if full coverage and accurate LULC data was a requirement for a project, then OSM data (at present) may not be the best option. However for certain land use classes, where the LULC information was available it was mostly correct so depending on project requirements OSM data may be a suitable alternative.

As we’ve said many times before on Spatial Reserves, it is not whether the data are good, but rather if they are good enough to meet your requirements.

Ref:
Dorn, H.,Törnros, T. and Zipf, A. (2015). Quality Evaluation of VGI Using Authoritative Data—A Comparison with Land Use Data in Southern Germany. ISPRS Int. J. Geo-Inf. 4, pp. 1657 – 1670

CropScape: Agricultural Data Portal and Analysis

August 18, 2013 Leave a comment

As we explain in our book, The GIS Guide to Public Domain Data, agriculture data is available in an increasing number of formats and portals.  One of these portals and an extremely useful one is called CropScape.  CropScape hosts the Cropland Data Layer (CDL), a raster geo-referenced land cover data product created annually for the continental USA using moderate resolution satellite imagery but also extensive agricultural ground truthing.

Cropscape Agricultural Portal

The Cropscape Agricultural Portal.

CropScape allows the data user to browse crop data spatially and temporally from 1997 each year to the present.  Tools include the ability to swipe images of two different years in the map panel, the ability to access agricultural census data by county, and identify crops at individual pixels.  But probably most importantly, CropScape allows the data user to download crop data in a Geotiff format for any customized area of interest.  The data set is also available each year back to 2008 as a zip file for the entire USA.  This data set is over 1 GB in size.  Statistics range from grapes to pumpkins and much more, but the primary focus is on large area summer crops such as wheat and corn.  The spatial resolution is 30 meters.  The interface is fairly intuitive but if additional assistance is needed, an extensive FAQ exists.

As we discuss in our book, a great many well-intentioned data portals exist, but many are not designed with the data analyst in mind.   CropScape is definitely designed from the data and GIS analyst’s perspective, which is welcome given the importance of and need for agricultural data.