add single file STAC extension

extensions/README.md

@@ -54,12 +54,8 @@ An extension can add new fields to STAC entities (content extension), or can add
 | [Label](label/README.md) (`label`)                           | Item             | Items that relate labeled AOIs with source imagery | *Proposal* |
 | [Point Cloud](pointcloud/README.md) (`pc`)                   | Item             | Provides a way to describe point cloud datasets. The point clouds can come from either active or passive sensors, and data is frequently acquired using tools such as LiDAR or coincidence-matched imagery. | *Proposal* |
 | [SAR](sar/README.md) (`sar`)                                 | Item             | Covers synthetic-aperture radar data that represents a snapshot of the earth for a single date and time. | *Proposal* |
-<<<<<<< HEAD
-| [Scientific](scientific/README.md) (`sci`)                   | Item             | Scientific metadata is considered to be data that indicate from which publication data originates and how the data itself should be cited or referenced. | *Proposal* |
-| [Single File STAC](single-file-stac/README.md) (-)                   | Catloag +Collection +Item | An extension to provide a set of Collections and Items as a single file catalog. | *Proposal* |
-=======
 | [Scientific](scientific/README.md) (`sci`)                   | Item +Collection | Scientific metadata is considered to be data that indicate from which publication data originates and how the data itself should be cited or referenced. | *Proposal* |
->>>>>>> a76d904270c4a369582b2319daa655e97d3f1b02
+| [Single File STAC](single-file-stac/README.md) (-)           | Catalog +Collection +Item | An extension to provide a set of Collections and Items as a single file catalog. | *Proposal* |
 
 ## Third-party / vendor extensions
 

extensions/single-file-stac/README.md

@@ -2,14 +2,16 @@
 
 **Extension [Maturity Classification](../README.md#extension-maturity): Proposal**
 
-An extension to provide a set of Collections and Items as a single file catalog.
+An extension to provide a set of Collections and Items as a single file catalog. The single file is a self contained catalog that contains everything that would normally be in a linked set of STAC files. This format is useful to save a portion of a catalog, or when creating a small catalog from derived data that should remain portable. It is most useful for saving the results of a search from a STAC API, as the Items, Collections, and optionally the search parameters are all saved within the single file. Hierarchical links have no meaning in a single file STAC, and so, if present, should be removed when creating a single file catalog.
+
+The Items in the single file catalog should not be merged with the Collection properties (i.e., common properties). The Collections are all included in the file as well, so there is no need to duplicate the common properties for every Item in the catalog.
 
 - [Example](examples/example.json)
 - [JSON Schema](json-schema/schema.json)
 
 ## Catalog fields
 
-A Single File STAC is a complete STAC catalog contained in a single file. It is sometimes useful to save a portion of a catalog (such as gained through a search) as single file so it is more portable than a set of linked files.
+A Single File STAC is a complete STAC catalog contained in a single file. 
 
 A Single File STAC is an [ItemCollection Object](../../item-spec/itemcollection-spec.md). This GeoJSON FeatureCollection has Features which are Items, but the Collections are still needed.