<title>Raster Overviews</title>
<para><varname>raster_overviews</varname> catalogs information about raster table columns used for overviews and additional information about them that is useful to know when utilizing overviews. Overview tables are cataloged in both <varname>raster_columns</varname> and <varname>raster_overviews</varname> because they are rasters in their own right but also serve an additional special purpose of being a lower resolution caricature of a higher resolution table. These are generated along-side the main raster table when you use the <varname>-l</varname> switch in raster loading.</para>
<para>Overview tables contain the same constraints as other raster tables as well as additional informational only constraints specific to overviews.</para>
- <note><para>The informaiton in <varname>raster_overviews</varname> does not duplicate the information in <varname>raster_columns</varname>. IF you need the information about an overview table present in <varname>raster_columns</varname> you can join the <varname>raster_overviews</varname> and <varname>raster_columns</varname> vuews together to get the full set of information you need.</para> </note>
+ <note><para>The information in <varname>raster_overviews</varname> does not duplicate the information in <varname>raster_columns</varname>. If you need the information about an overview table present in <varname>raster_columns</varname> you can join the <varname>raster_overviews</varname> and <varname>raster_columns</varname> vuews together by to get the full set of information you need.</para> </note>
<para>Two main reasons for overviews are:</para>
<orderedlist>
<listitem>Low resolution representation of the core tables commonly used for fast mapping zoom-out.</listitem>
<para><varname>overview_factor</varname> - this is the pyramid level of the overview table. The higher the number the lower the resolution of the table.</para>
</listitem>
</itemizedlist>
+
</sect2>
</sect1>
</chapter>