Let's be coherent with plural form of "data"

docs/gentle_gis_introduction/introducing_gis.rst

@@ -246,7 +246,7 @@ data associated with places.
 
 GIS Systems work with many different types of data. **Vector data** is stored as
 a series of ``X, Y`` coordinate pairs inside the computer's memory. Vector data
-is used to represent points, lines and areas. Illustration :numref:`figure_vector_data`
+are used to represent points, lines and areas. Illustration :numref:`figure_vector_data`
 shows different types of vector data being viewed in a GIS application. In the
 tutorials that follow we will be exploring vector data in more detail.
 
@@ -256,7 +256,7 @@ tutorials that follow we will be exploring vector data in more detail.
    :align: center
    :width: 30em
 
-   Vector data is used to represent points (e.g., towns), lines (e.g., rivers) and
+   Vector data are used to represent points (e.g., towns), lines (e.g., rivers) and
    polygons (e.g., municipal boundaries).
 
 **Raster data** are stored as a grid of values. There are many satellites circling