rename parameter sections, add Collections section

Author: letmaik

SUMMARY.md

@@ -15,9 +15,9 @@
   * [Categorical Parameters](parameter-categories.md)
   * [Parameter Groups](parameter-groups.md)
 * [Parameter Examples](parameter-examples.md)
-  * [Argo Quality Flags](parameter-argo-quality-flags.md)
-  * [Sea Ice Area Fraction](parameter-sea-ice-area-fraction.md)
-* [Collections](collection.md)
+  * [Quality Flags](parameter-quality-flags.md)
+  * [Fractional Quantities](parameter-fractional-quantities.md)
+* [Collections](collections.md)
 * [Encoding Advice](encoding-advice.md)
 * [Extensions](extensions.md)
   * [Custom Fields](custom-fields.md)

collections.md

@@ -0,0 +1,102 @@
+# Collections
+
+CoverageJSON has a compact coverage collection structure which allows to move repeated information like parameters and reference systems to the collection level. It is especially useful for uniform collections but can also be used for any other collection where each coverage may have a different set of parameters or reference systems.
+
+Example:
+
+```json
+{
+  "type" : "CoverageCollection",
+  "domainType" : "VerticalProfile",
+  "parameters" : {
+    "PSAL": {
+      "type" : "Parameter",
+      "description" : {
+        "en": "The measured salinity, in practical salinity units (psu) of the sea water"
+      },
+      "unit" : {
+        "symbol" : "psu"
+      },
+      "observedProperty" : {
+        "id": "http://vocab.nerc.ac.uk/standard_name/sea_water_salinity/",
+        "label" : {
+          "en": "Sea Water Salinity"
+        }
+      }
+    }
+  },
+  "referencing": [{
+    "components": ["x","y"],
+    "system": {
+      "type": "GeodeticCRS",
+      "id": "http://www.opengis.net/def/crs/OGC/1.3/CRS84"
+    }
+  }, {
+    "components": ["z"],
+    "system": {
+      "type": "VerticalCRS",
+      "cs": {
+        "axes": [{
+          "name": {
+            "en": "Pressure"
+          },
+          "direction": "down",
+          "unit": {
+            "symbol": "Pa"
+          }
+        }]
+      }
+    }
+  }, {
+    "components": ["t"],
+    "system": {
+      "type": "TemporalRS",
+      "calendar": "Gregorian"
+    }
+  }],
+  "coverages": [
+    {
+      "type" : "Coverage",
+      "domain" : {
+        "type": "Domain",
+        "axes": {
+          "x": { "values": [-10.1] },
+          "y": { "values": [-40.2] },
+          "z": { "values": [ 5, 8, 14 ] },
+          "t": { "values": ["2013-01-13T11:12:20Z"] }
+        }
+      },
+      "ranges" : {
+        "PSAL" : {
+          "type" : "NdArray",
+          "dataType": "float",
+          "shape": [3],
+          "axisNames": ["z"],
+          "values" : [ 43.7, 43.8, 43.9 ]
+        }
+      }
+    }, {
+      "type" : "Coverage",
+      "domain" : {
+        "type": "Domain",
+        "axes": {
+          "x": { "values": [-11.1] },
+          "y": { "values": [-45.2] },
+          "z": { "values": [ 4, 7, 9 ] },
+          "t": { "values": ["2013-01-13T12:12:20Z"] }
+        }
+      },
+      "ranges" : {
+        "PSAL" : {
+          "type" : "NdArray",
+          "dataType": "float",
+          "shape": [3],
+          "axisNames": ["z"],
+          "values" : [ 42.7, 41.8, 40.9 ]
+        }
+      }
+    }]
+}
+```
+
+For more details, see the [Collection](https://covjson.org/spec/#coverage-collection-objects) section of the specification.

parameter-sea-ice-area-fraction.md renamed to parameter-fractional-quantities.md

@@ -1,6 +1,6 @@
-# Sea Ice Area Fraction
+# Fractional Quantities
 
-In this example we will see how a fraction can be represented in CovJSON. For that we use the sea ice area fraction.
+In this example we will see how a fractional quantity can be represented in CovJSON. For that we use the sea ice area fraction.
 
 Fractions in CovJSON are stored as a decimal number which is typically between 0 and 1. Percentages are fractions comparing a number to 100, which means they simply have a unit of `1/100`, which is often symbolized with the percentage sign `%`. Depending on how data values are stored, those two cases have to be distinguished.
 

parameter-argo-quality-flags.md renamed to parameter-quality-flags.md

@@ -1,6 +1,6 @@
 {% from "macros.md" import playgroundLink %}
 
-# Argo Quality Flags
+# Quality Flags
 
 Quality flags in CovJSON are represented with a categorical parameter. In this example we use the [Argo quality flags](http://mmisw.org/ont/argo/qualityFlag):