sample record, PGIFv2 (Pelagios Gazetteer Interconnection Format); comments requested, spec and more examples soon

map.geojson

{
  "type": "Feature",
  "labels": [
    {
      "value": "Athens",
      "lang": "en"
    }
  ],
  "properties": {
    "label": "Athens",
    "id": "p1234",
    "uri": "http://mygaz.org/places/p1234",
    "prop_012": ""
  },
  "description": {
    "value": "A major Greek city-state",
    "lang": "en",
    "source": "uri"
  },
  "modern_countries": [
    "GR"
  ],
  "when": {
    "timespans": [
      {
        "start": {
          "in": "-0750"
        },
        "end": {
          "in": "0640"
        }
      }
    ],
    "periods": [
      {
        "name": "",
        "uri": "http://n2t.net/ark:/99152/p03wskd389m"
      }
    ],
    "label": ""
  },
  "names": [
    {
      "name": "Athenae",
      "hasAttestation": "uri",
      "lang": "el-ltn",
      "when": {}
    },
    {
      "name": "Αθήνα",
      "lang": "el",
      "hasAttestation": {
        "publisher": "uri",
        "evidence": "uri",
        "chars": "Αθήνα"
      }
    }
  ],
  "geometry": {
    "type": "GeometryCollection",
    "geometries": [
      {
        "type": "Point",
        "coordinates": [
          23.73,
          37.98
        ],
        "when": {
          "periods": [
            {
              "label": "",
              "uri": ""
            }
          ]
        },
        "source": {
          "label": "The Atlas of ___",
          "uri": ""
        },
        "representative": "True"
      },
      {
        "type": "Polygon",
        "coordinates": [
          [
            [
              23.68,
              37.93
            ],
            [
              23.77,
              37.93
            ],
            [
              23.77,
              38.03
            ],
            [
              23.68,
              38.03
            ],
            [
              23.68,
              37.93
            ]
          ]
        ],
        "when": {
          "label": "",
          "timespans": [
            {
              "start": {
                "in": "nnnn-nn"
              },
              "end": {
                "earliest": "nnnn",
                "latest": "nnnn-nn-nn"
              }
            }
          ]
        },
        "source": {
          "label": "The Atlas of ___",
          "uri": ""
        }
      }
    ]
  },
  "types": [
    {
      "label": "inhabited place",
      "lang": "en",
      "uri": "http://vocab.getty.edu/page/aat/300008347"
    }
  ],
  "part_of": [
    {
      "parent": "uri",
      "when": {
        "timespans": [
          {
            "start": {
              "in": "nnnn"
            },
            "end": {
              "earliest": "-nnnn",
              "latest": "nnnn"
            }
          }
        ],
        "duration": "~200y"
      },
      "label": "for approx. 200 years, sometime between {start} and {end}",
      "source": "uri"
    },
    {
      "parent": "uri",
      "when": {
        "when": {
          "periods": [
            {
              "label": "",
              "uri": ""
            },
            {
              "label": "",
              "uri": ""
            }
          ]
        }
      },
      "label": "roughly during the {x} and {y} periods",
      "source": "uri"
    }
  ],
  "related": [
    {
      "type": "exactMatch",
      "uri": ""
    },
    {
      "type": "closeMatch",
      "uri": ""
    },
    {
      "type": "primaryTopicOf",
      "uri": ""
    },
    {
      "type": "seeAlso",
      "uri": ""
    }
  ]
}

PGIFv2 is an implementation of GeoJSON-T, a proposed extension to GeoJSON adding "when."