docs: land height is "elevation", not "altitude"

See https://mapscaping.com/blogs/geo-candy/what-is-the-difference-between-elevation-relief-and-altitude
No patching of regression tests.

Reported-by: taf1@cornell.edu

Discussion: https://postgr.es/m/158506544539.679.2278386310645558048@wrigleys.postgresql.org

Backpatch-through: 9.5

doc/src/sgml/advanced.sgml

@@ -585,20 +585,20 @@ SELECT sum(salary) OVER w, avg(salary) OVER w
 CREATE TABLE capitals (
   name       text,
   population real,
-  altitude   int,    -- (in ft)
+  elevation  int,    -- (in ft)
   state      char(2)
 );
 
 CREATE TABLE non_capitals (
   name       text,
   population real,
-  altitude   int     -- (in ft)
+  elevation  int     -- (in ft)
 );
 
 CREATE VIEW cities AS
-  SELECT name, population, altitude FROM capitals
+  SELECT name, population, elevation FROM capitals
     UNION
-  SELECT name, population, altitude FROM non_capitals;
+  SELECT name, population, elevation FROM non_capitals;
 </programlisting>
 
     This works OK as far as querying goes, but it gets ugly when you
@@ -612,7 +612,7 @@ CREATE VIEW cities AS
 CREATE TABLE cities (
   name       text,
   population real,
-  altitude   int     -- (in ft)
+  elevation  int     -- (in ft)
 );
 
 CREATE TABLE capitals (
@@ -624,7 +624,7 @@ CREATE TABLE capitals (
    <para>
     In this case, a row of <classname>capitals</classname>
     <firstterm>inherits</firstterm> all columns (<structfield>name</structfield>,
-    <structfield>population</structfield>, and <structfield>altitude</structfield>) from its
+    <structfield>population</structfield>, and <structfield>elevation</structfield>) from its
     <firstterm>parent</firstterm>, <classname>cities</classname>.  The
     type of the column <structfield>name</structfield> is
     <type>text</type>, a native <productname>PostgreSQL</productname>
@@ -636,23 +636,23 @@ CREATE TABLE capitals (
 
    <para>
     For example, the  following  query finds the  names  of  all  cities,
-    including  state capitals, that are located at an altitude
+    including  state capitals, that are located at an elevation
     over 500 feet:
 
 <programlisting>
-SELECT name, altitude
+SELECT name, elevation
   FROM cities
-  WHERE altitude &gt; 500;
+  WHERE elevation &gt; 500;
 </programlisting>
 
     which returns:
 
 <screen>
-   name    | altitude
------------+----------
- Las Vegas |     2174
- Mariposa  |     1953
- Madison   |      845
+   name    | elevation
+-----------+-----------
+ Las Vegas |      2174
+ Mariposa  |      1953
+ Madison   |       845
 (3 rows)
 </screen>
    </para>
@@ -660,19 +660,19 @@ SELECT name, altitude
    <para>
     On the other hand, the  following  query  finds
     all  the cities that are not state capitals and
-    are situated at an altitude over 500 feet:
+    are situated at an elevation over 500 feet:
 
 <programlisting>
-SELECT name, altitude
+SELECT name, elevation
     FROM ONLY cities
-    WHERE altitude &gt; 500;
+    WHERE elevation &gt; 500;
 </programlisting>
 
 <screen>
-   name    | altitude
------------+----------
- Las Vegas |     2174
- Mariposa  |     1953
+   name    | elevation
+-----------+-----------
+ Las Vegas |      2174
+ Mariposa  |      1953
 (2 rows)
 </screen>
    </para>