NASA Earthdata was the second platform in the open-data series I shared before my GIS session. I wanted to introduce more than a place to download a map: it provides access to many Earth science products spanning atmosphere, land, oceans and climate. I focused on digital elevation because one well-understood layer can contribute to several different environmental questions.
What Earthdata offers
Products concern temperature, rainfall, vegetation, air quality, ice, sea level and many other topics. Each has its own definition, source, coverage and period. The Earthdata name alone does not establish identical accuracy, currency or purpose across all files. [1]
I therefore begin with the required variable and suitable product, not the first downloadable result. Some products update regularly; others reprocess historical observations. That distinction matters when moving from general satellite-data discussion to a specific elevation product.
What a digital elevation model represents
A DEM is a numerical grid whose cell values represent elevation according to the product definition. It supports interpretation of hills, depressions and slopes and the derivation of further layers. It is a representation of terrain, not a detailed survey of every point.
The represented surface also matters. Buildings and vegetation influence some products, while others aim to represent bare earth. The appropriate choice depends on whether the task concerns regional analysis, model preparation or a decision requiring finer detail.
Biodiversity: putting observations in terrain context
Occurrence locations can be connected with elevation and slope to examine whether records are associated with particular terrain ranges. The map then helps ask not only where a species was recorded, but what characterises those locations.
The pattern still needs interpretation. Records may cluster at accessible elevations or where survey effort was concentrated. Terrain should be considered with habitat, date and sampling information rather than treating spatial association as proof of the cause of distribution.
Water and soil applications
Elevation can support drainage-direction and catchment analysis, with derived layers contributing to hydrological or hydraulic preparation and flood assessment. Delineating a basin on screen does not complete a dam design or flood estimate; additional methods and evidence are required.
Slope and landform can also contribute to understanding erosion alongside rainfall, cover, soil properties and management. The DEM supplies the terrain component of the system rather than replacing all its other controls.
Local climate, visibility and air quality
Elevation can be studied alongside temperature or rainfall to examine local climatic relationships. Viewshed analysis supports visibility and landscape questions according to the surface representation and assumed observer and target heights.
Terrain also forms part of the environment represented in air dispersion work and may require processing for the selected model. The same dataset can therefore support different tasks, while each application introduces its own assumptions and additional inputs.
Contours and hillshade
Contours connect equal elevations, while hillshade uses simulated illumination to make landform easier to read. These outputs help communicate terrain and combine it with occurrence and land-cover layers in a GIS project.
Improved presentation does not create improved accuracy. Closely spaced contours cannot add information missing from the source grid, and smoothing does not turn it into a better survey. Contour interval and display scale should suit the evidence and purpose, with processing retained.
Read the SRTM product definition
SRTM products have different specifications. The global one-arc-second product is approximately 30 metres, with the mission’s core land coverage between about 60° N and 56° S. Observations date to the 2000 mission; a later distribution or processing release does not imply newly measured terrain. [2]
Grid spacing is not vertical accuracy. Nor should SRTM30 automatically be read as 30 metres; the name can refer to 30 arc seconds. Preserve the full product name, units, vertical reference, void information and quality description, because a mistaken definition affects every derived layer.
A practical route into the study
Define the area and product, read its documentation and use an Earthdata account where the access service requires authentication. After download, check coordinates, elevations and gaps, document mosaicking or clipping, and derive the terrain layers needed by the question.
In the session we combined this work with GBIF biodiversity records and Copernicus land cover. Elevation then became part of an integrated examination of landform, observations and activity, rather than a contour map produced only for display.
References & original writing
Adapted and expanded from the author’s LinkedIn writing. Technical references are listed below.
