geographic data: sources and considerations. geographical concepts: geographic coordinate system:...
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Geographic data: sources and considerations
Geographical Concepts:
• Geographic coordinate system: defines locations on the earth using an angular unit of measure, a prime meridian, and a datum
- datum: defines the position of the origin and the orientation of latitude and longitude lines
• Map projection: mathematical transformation of the three-dimensional surface of the earth into a flat map sheet
Types of spatial data in GIS
• Vector data: points, lines, polygons (shapefiles)
• Raster data: used in ecological niche modeling for representing environmental conditions (grids)
Example of interpolated surface from point data using Inverse Distance Weighting technique. Courtesy: Science Applications International Corporation
Raster obtained through interpolation Raster obtained through remote sensing
Characteristics of geographic data
• Quality: →Interpolated vs. remotely sensed
→Scale at which interpolation was done
• Spatial resolution – has to match the scale of the
questions we try to address with ENM
• Temporal resolution: can represent daily,
monthly, annual, or multi-annual averages
• Type: categorical vs. continuous (some
ecological niche modeling algorithms don't work
well with categorical data)
1.Quality: interpolation
WorldClim dataset: locations of climate stations with precipitation data - 47,554 stations
IPPC climate dataset: precipitation data from 19,800 stations
Mean annual precipitation (1960-1990)
WorldClim 1.4
2. Spatial resolution
• size of the cells in the raster
IPPC mean annual precipitation 0.5° resolution WorldClim mean annual precipitation 0.008° resolution
Florida panhandle
3. Temporal resolution
• time period averaged (days, months, decades, etc)
MODIS EVI 15-30 October MODIS EVI 30 October-15November
NASA/GSFC/University of Arizona
Climate projections
Past climate scenarios (e.g. Pleistocene)
Future climate scenarios
Mean maximum temperature (1960-1990)
4. Type• Continuous data – surfaces, used for natural (physical phenomena); the values are assigned to the points and represent the actual measured value
Land cover 2000
• Categorical data – correspond to discrete fields; the values are assigned to the entire cell area and represent the category number
Digital elevation model
Points to keep in mind when selecting geographic data for ENM
• Temporal and spatial resolution of geographic data has to match those of species occurrence data; also, select a spatial resolution that matches the question asked (e.g. continental spread of an invasive species, vs. predicted distribution of a local endemic species)
• Categorical data doesn’t work well with some niche modeling algorithms; it is also difficult to match its temporal resolution with occurrence data
• Remotely sensed data is powerful (no interpolation), but can only be used with recent, up to date, species occurrence datasets
• When downloading geographic data, pay attention to projection and datum, and any metadata available; some transformations may be necessary
Sources of data
•Climatic (Global) data:
WorldClim current (1960-1990) climate data http://www.worldclim.org/
IPCC current and future climate datahttp://www.ipcc-data.org/obs/get_30yr_means.htmlhttp://www.ipcc-data.org/ddc_climscen.html
Climatic Research Unit http://www.cru.uea.ac.uk/cru/data/hrg.htm
Paleoreconstructions PMIP http://pmip.lsce.ipsl.fr/NOAA: http://www.ncdc.noaa.gov/paleo/
Sources of data
•Topographic and bathymetric:
USGS Hydro 1k http://edc.usgs.gov/products/elevation/gtopo30/hydro/
NOAA ETOPO www.ngdc.noaa.gov/mgg/global/seltopo.htmlBathymetry http://ibis.grdl.noaa.gov/cgi-bin/bathy/bathD.pl
•Marine data:
NOAA World Ocean Atlas http://www.nodc.noaa.gov/OC5/indprod.html
Climate Prediction Center http://www.cpc.noaa.gov/products/predictions/30day/SSTs/sst_clim.html
•Satellite-derived (free):
Global Vegetation Indices:
MODIS http://edcdaac.usgs.gov/dataproducts.asp(EVI and NDVI) 2000 to present
AVHRR http://edcsns17.cr.usgs.gov/1KM/1kmhomepage.html(NDVI): 1985 to present
Global Land Cover:
IES Global Landcover 2000 http://www-gvm.jrc.it/glc2000/
University of Maryland (1992) http://glcf.umiacs.umd.edu/data/
Sources of data
Other data
WWF Ecoregions http://www.worldwildlife.org/science/data.cfm
UNEP IUCN Protected Areas http://sea.unep-wcmc.org/wdbpa/