Revise intro of README and fix example query links

In collaboration with @Qup42

README.md

@@ -1,10 +1,9 @@
 [![Build](https://github.com/ad-freiburg/qlever-petrimaps/actions/workflows/build.yml/badge.svg)](https://github.com/ad-freiburg/qlever-petrimaps/actions/workflows/build.yml)
-# QLever petrimaps
+# QLever Petrimaps
 
-Visualization of geospatial SPARQL query results for QLever on a map, either as individual objects or as a heatmap. Can handle hundreds of millions of result rows, tested with over 200 million results (all streets in OSM). Implemented as a middle-end / middleware.
-This is still very much hacked-together, use with care.
+Interactive visualization of SPARQL query results with geospatial information on a map, either as individual objects or as a heatmap. Petrimaps can display **hundreds of millions of objects** interactively, for example, a heatmap of all the streets in a given country, or even in the whole world. Petrimaps is implemented as a middleware. In the [QLever UI](https://github.com/ad-freiburg/qlever-ui), whenever a SPARQL result has WKT literals in its last column, a "Map view" button is displayed, which leads to an instance of Petrimaps.
 
-Examples: [All railway lines in OSM](http://qlever.cs.uni-freiburg.de/mapui-petri/?query=PREFIX+rdf%3A+%3Chttp%3A%2F%2Fwww.w3.org%2F1999%2F02%2F22-rdf-syntax-ns%23%3E+PREFIX+geo%3A+%3Chttp%3A%2F%2Fwww.opengis.net%2Font%2Fgeosparql%23%3E+PREFIX+osmkey%3A+%3Chttps%3A%2F%2Fwww.openstreetmap.org%2Fwiki%2FKey%3A%3E+PREFIX+osm%3A+%3Chttps%3A%2F%2Fwww.openstreetmap.org%2F%3E+PREFIX+rdf%3A+%3Chttp%3A%2F%2Fwww.w3.org%2F1999%2F02%2F22-rdf-syntax-ns%23%3E+SELECT+%3Fosm_id+%3Fgeometry+WHERE+%7B+%3Fosm_id+osmkey%3Arailway+%3Frail+.+%3Fosm_id+rdf%3Atype+osm%3Away+.+%3Fosm_id+geo%3AhasGeometry%2Fgeo%3AasWKT+%3Fgeometry+%7D&backend=https%3A%2F%2Fqlever.cs.uni-freiburg.de%2Fapi%2Fosm-planet), [All buildings in Germany in OSM](http://qlever.cs.uni-freiburg.de/mapui-petri/?query=PREFIX%20geo%3A%20%3Chttp%3A%2F%2Fwww.opengis.net%2Font%2Fgeosparql%23%3E%20PREFIX%20osmkey%3A%20%3Chttps%3A%2F%2Fwww.openstreetmap.org%2Fwiki%2FKey%3A%3E%20PREFIX%20ogc%3A%20%3Chttp%3A%2F%2Fwww.opengis.net%2Frdf%23%3E%20PREFIX%20osmrel%3A%20%3Chttps%3A%2F%2Fwww.openstreetmap.org%2Frelation%2F%3E%20SELECT%20%3Fosm_id%20%3Fhasgeometry%20WHERE%20%7B%20osmrel%3A51477%20ogc%3AsfContains%20%3Fosm_id%20.%20%3Fosm_id%20geo%3AhasGeometry%2Fgeo%3AasWKT%20%3Fhasgeometry%20.%20%3Fosm_id%20osmkey%3Abuilding%20%3Fbuilding%20%7D&backend=https%3A%2F%2Fqlever.cs.uni-freiburg.de%2Fapi%2Fosm-planet)
+Here are two example queries: [All railway lines in OSM](https://qlever.cs.uni-freiburg.de/petrimaps/?query=PREFIX+rdf%3A+%3Chttp%3A%2F%2Fwww.w3.org%2F1999%2F02%2F22-rdf-syntax-ns%23%3E+PREFIX+geo%3A+%3Chttp%3A%2F%2Fwww.opengis.net%2Font%2Fgeosparql%23%3E+PREFIX+osmkey%3A+%3Chttps%3A%2F%2Fwww.openstreetmap.org%2Fwiki%2FKey%3A%3E+PREFIX+osm%3A+%3Chttps%3A%2F%2Fwww.openstreetmap.org%2F%3E+PREFIX+rdf%3A+%3Chttp%3A%2F%2Fwww.w3.org%2F1999%2F02%2F22-rdf-syntax-ns%23%3E+SELECT+%3Fosm_id+%3Fgeometry+WHERE+%7B+%3Fosm_id+osmkey%3Arailway+%3Frail+.+%3Fosm_id+rdf%3Atype+osm%3Away+.+%3Fosm_id+geo%3AhasGeometry%2Fgeo%3AasWKT+%3Fgeometry+%7D&backend=https%3A%2F%2Fqlever.cs.uni-freiburg.de%2Fapi%2Fosm-planet), [All streets in Germany in OSM](https://qlever.cs.uni-freiburg.de/petrimaps/?query=PREFIX+ogc%3A+%3Chttp%3A%2F%2Fwww.opengis.net%2Frdf%23%3E+PREFIX+osmrel%3A+%3Chttps%3A%2F%2Fwww.openstreetmap.org%2Frelation%2F%3E+PREFIX+geo%3A+%3Chttp%3A%2F%2Fwww.opengis.net%2Font%2Fgeosparql%23%3E+PREFIX+osm%3A+%3Chttps%3A%2F%2Fwww.openstreetmap.org%2F%3E+PREFIX+rdf%3A+%3Chttp%3A%2F%2Fwww.w3.org%2F1999%2F02%2F22-rdf-syntax-ns%23%3E+PREFIX+osmkey%3A+%3Chttps%3A%2F%2Fwww.openstreetmap.org%2Fwiki%2FKey%3A%3E+SELECT+%3Fosm_id+%3Fshape+WHERE+%7B+osmrel%3A51477+ogc%3AsfContains+%3Fosm_id+.+%3Fosm_id+osmkey%3Ahighway+%3Fhighway+.+%3Fosm_id+rdf%3Atype+osm%3Away+.+%3Fosm_id+geo%3AhasGeometry%2Fgeo%3AasWKT+%3Fshape+%7D&backend=https%3A%2F%2Fqlever.cs.uni-freiburg.de%2Fapi%2Fosm-planet).
 
 ## Requirements
 * gcc > 5.0 || clang > 3.9