For datasets produced by the GIS Lab at Baruch College, we create Dublin Core metadata records expressed in XML. Our records use a subset of the DC elements and terms that we have specified as requirements for all metadata we create, and we follow best practices used by the Open Geoportal and GeoBlacklight communities. We follow an in-house data application profile that specifies formats and controlled vocabularies (drawn from ISO 19115 topics, GeoBlacklight, geonames, Dublin Core, and others). We check our records against this profile, validate them against our XML schema, and style them for presentation with a CSS stylesheet. Click on any metadata XML link provided on the download pages for our Datasets for examples. We adopted this standard in spring 2020 and will be converting our old records as we update each dataset.
Visit our GitHub GIS Lab Metadata page for more information and to access our profile, schema, and scripts. There's also an older repository with resources that we previously used for verifying ISO 19139 metadata.
For resources that we purchase or subscribe to (i.e. that we do not create), metadata is provided by that source and comes in various standards and formats.