Add information about proj.db. (#1491)

3 files changed, 31 insertions, 5 deletions

diff --git a/docs/source/faq.rst b/docs/source/faq.rst
index e6a2e54a..e7265d48 100644
--- a/docs/source/faq.rst
+++ b/docs/source/faq.rst
@@ -156,3 +156,19 @@ of the Well-Known Text output:
             AREA["World"],
             BBOX[-90,-180,90,180]],
         ID["EPSG",4326]]
+
+Why am I getting the error "Cannot find proj.db"?
+--------------------------------------------------------------------------------
+The file :ref:`proj.db<proj-db>` must be readable for the library to properly
+function.  Like other :doc:`resource files<../resource_files>`,
+it is located using a set of search
+paths.  In most cases, the following paths are checked in order:
+
+    - A path provided by the environment variable :envvar:`PROJ_LIB`.
+    - A path built into PROJ as its resource installation directory
+      (typically ../share/proj relative to the PROJ library).
+    - The current directory.
+
+Note that if you're using conda, activating an environment sets
+:envvar:`PROJ_LIB` to a resource directory located in that environment.
+
diff --git a/docs/source/resource_files.rst b/docs/source/resource_files.rst
index d6f64175..9eecb9ea 100644
--- a/docs/source/resource_files.rst
+++ b/docs/source/resource_files.rst
@@ -14,6 +14,15 @@ In addition to the bundled init-files the PROJ.4 project also distribute a numbe
 of packages containing transformation grids and additional init-files not included
 in the main PROJ package.
 
+.. _proj-db:
+
+proj.db
+-------------------------------------------------------------------------------
+
+A proj installation includes a SQLite database of transformation information
+that must be accessible for the library to work properly.  The library will
+print an error if the database can't be found.
+
 External resources
 -------------------------------------------------------------------------------
 
@@ -36,7 +45,7 @@ At the moment three regional resource file packages are distributed:
 
 * `Europe <https://github.com/OSGeo/proj-datumgrid/tree/master/europe#proj-datumgrid-europe>`_
 * `Oceania <https://github.com/OSGeo/proj-datumgrid/tree/master/oceania#proj-datumgrid-oceania>`_
-* `North America <https://github.com/OSGeo/proj-datumgrid/tree/master/north-america#proj-datumgrid-north-america>`_ 
+* `North America <https://github.com/OSGeo/proj-datumgrid/tree/master/north-america#proj-datumgrid-north-america>`_
 
 Click the links to jump to the relevant README files for each package. Details
 on the content of the packages maintained there.
diff --git a/docs/source/usage/environmentvars.rst b/docs/source/usage/environmentvars.rst
index c8dfe28e..457432a0 100644
--- a/docs/source/usage/environmentvars.rst
+++ b/docs/source/usage/environmentvars.rst
@@ -37,15 +37,16 @@ done by setting the variable with no content::
     character.
 
     PROJ is hardcoded to look for resource files
-    in other locations as well, amongst those are the users home directory,
-    ``/usr/share/proj`` and the current folder.
+    in other locations as well, amongst those are the
+    installation directory (usually ``share/proj`` under the PROJ
+    installation root) and the current folder.
 
-    You can also set the location of the resource files using 
+    You can also set the location of the resource files using
     :func:`proj_context_set_search_paths` in the `proj.h` API header.
 
 .. versionchanged:: 6.1.0
 
-    Starting with PROJ version 6.1.0, the paths set by 
+    Starting with PROJ version 6.1.0, the paths set by
     :func:`proj_context_set_search_paths` will have priority over the
     :envvar:`PROJ_LIB` to allow for mutliple versions of PROJ
     resource files on your system without conflicting.