Navigating ENVO
Large ontologies such as ENVO can be difficult to understand or navigate upon first glance. As such we have created this guide about how to navigate envo, as well as what types of classes exists within the ontology.
The simplest way to browse ENVO is through the Ontology Lookup Service (OLS) envo browser. In the OLS web browser you can search for terms by their labels (or identifiers). For example, typing in rock, one would see the following:
Clicking on a term such as rock you'll get the following:
You can use OLS to further explore a terms subclasses in the Tree view tab. You can expand or collapse a sub-hierarchy by clicking on the 
sign next to a term. From there you can continue to explore the hierarchy by expanding and collapsing sub-hierarchies.
A more advanced way to browse ENVO, which enables users to view and drill down on the entire file at once is to download protégé.
Once installed click File, then Open from URL....
Then in the URI box paste in http://purl.obolibrary.org/obo/envo.owl, and click OK.
Next click on the Entities tab.
You can click on the small triangles 
next to terms in order to expand or collapse them to show or hide their subclasses.
The top level classes can be a little confusing to follow so see the ENVO Hierarchies section about where to navigate to in order to get started. At any time in protégé you can search for classes by name or ID, by typing control and f on windows or command and f on a mac. This will bring up a search box in which you can type into.
At the very top of the ENVO hierarchy you'll find the terms continuant and occurrent.
These terms are from the Basic Formal Ontology (BFO), which is the upper level ontology that ENVO uses. There are quite a few details about how BFO represents and divides up various concepts. The very top most level classes are explained as follows: Continuants are classes that don't change over time, e.g., a wine glass. Occurrents are classes which unfold overtime, e.g., a glass blowing process.
In order to keep things simple rather than explain more about BFO, the following sections highlight the important hierarchies within ENVO. These are the places to start when searching for ENVO terms.
The ENVO environmental material hierarchy contains classes representing materials found within environmental systems. Examples of material entity classes include: soil, sea water, and snow.
The ENVO astronomical body part hierarchy contains classes which represent parts of astronomical bodies which includes planets (such as Earth), stars or moons. Examples of (Earth-centric) astronomical body part classes include: plain, lake, and volcano.
The ENVO biome hierarchy classes represent ecosystems to which resident ecological communities have evolved adaptations. Examples of biome classes include: polar biome, marine pelagic biome, and tropical savanna biome.
For more generic system classes which do not account for ecological adaptations to a given set of conditions see the ENVO ecosystem, and environmental system hierarchies. Note that those classes are all under the system hierarchy.
The ENVO environmental system process hierarchy contains classes representing processes which occur within environmental systems. Examples of environmental system process classes include: erosion, ocean acidification, and lightning strike.
The ENVO physical object quality hierarchy contains classes which represent characteristics or attributes of physical materials. An example of a quality is the red color that we perceive when looking at this Red Delicious apple.
Examples of ENVO physical object quality classes include: porosity of soil, temperature of air, and concentration of phosphate in liquid water.
The ENVO: site hierarchy contains classes which refer to spatial areas or regions. Examples of site classes include: protected area, desert oasis and archeological site.
