fix image link and tweak description

_sources/features/topo-arc/examples.yaml

@@ -4,7 +4,7 @@
 
     Topology defined by 2 end points and a centre that are references to features with point geometry.
 
-    ![Example](assets/arc-with-center.png)
+    ![Example](assets/arc-by-center.png)
     
     radius and arcLength are implicit but may be provided as optional properties of the feature.
 

bblocks-config.yaml

@@ -1,16 +1,20 @@
 identifier-prefix: ogc.geo.topo.
 
 name: Topo-Feature
-abstract: Generalised Topology Between Identified Objects (Features)
+abstract: Features with geometry defined via  generalised topology between identified objects (Features).
 description: |
   Defines Feature (object) topology using a _topology_ property to reference an ordered list of references to other features. 
 
-  Other features may be either features with topology properties or GeoJSON (or FG-JSON) point objects.
+  Other features may be either features with topology properties or GeoJSON (or FG-JSON) geometry properties.
 
   Topo-Feature defined objects can be solids, swept volumes or any other concept. 
   
-  Note: This is a generalisation of the TopoJSON concept using inline data, (nested sets of coordinates) but not limited to self-contained geometries (i.e. it allows for general topology to be described between independent features (objects) with any geometry dimensions)
+  Topo-Feature allows for general topology to be described between independent features (objects) with any geometry dimensions. 
   
-  Topo-Feature doesnt use TopoJSON's coordinate compaction and transformation, however it does allow for explicit CRS, and coordinate compaction transformations could be defined as derived CRS if required.)
+  Topo-Feature-Collections define a self-contained set of such objects with referential integrity (all elements are present to fully define geometry coordinates.
+  
+  Note: This is a generalisation of the TopoJSON concept using inline, nested arrays of coordinates - but not limited to self-contained geometries per feature, duplicated between topologically related features.. 
+  
+  _Topo-Feature allows for explicit CRS. If desired coordinate compaction transformations could be defined as per TopoJSON functionality, using specialised CRS definition._