DOCSP-4345: [Charts] As an author, I can create a geo heatmap (#140)

* DOCSP-4345: [Charts] As an author, I can create a geo heatmap

Author: steveren

backups/charts-DOCSP-4581.json

@@ -19,5 +19,5 @@ Placeholder description for the Geospatial chart type.
    .. toctree::
       :titlesonly:
 
-.. sub-pages toc goes here
+      /chart-type-reference/geospatial-heatmap
 

backups/charts-v0.11.json

@@ -0,0 +1,78 @@
+==================
+Geospatial Heatmap
+==================
+
+.. default-domain:: mongodb
+
+.. contents:: On this page
+   :local:
+   :backlinks: none
+   :depth: 1
+   :class: singlecol
+
+Overview
+--------
+
+Geospatial heatmap charts are useful for displaying how
+geographical areas of a map compare to one another based on a given
+criterion.
+
+.. note::
+
+   Heatmap charts can use a maximum of 10,000 documents. If you
+   create a heatmap with a collection of more than 10,000
+   documents, turn on :ref:`Sample Mode <charts-sample-mode>` or use a
+   :ref:`filter <charts-filter-documents>`. Otherwise, your chart may
+   use incomplete or misleading data.
+
+To create a geospatial heatmap chart:
+
+1. On the chart editing screen, select :guilabel:`Geospatial` from
+   the :guilabel:`Chart Type` dropdown menu.
+
+#. Select :guilabel:`Heatmap` from the three available geospatial
+   chart types.
+
+Encoding Channels
+-----------------
+
+Coordinates
+~~~~~~~~~~~
+
+A :guilabel:`geopoint` encoding channel which defines the map
+area of the chart. See the :ref:`Geopoint <geopoint>` reference page
+for more information about what types of data you can use in this
+channel.
+
+Intensity
+~~~~~~~~~
+
+.. include:: /includes/intensity-definition.rst
+
+In geospatial heatmaps, values are aggregated within the radius
+specified in the :doc:`customization </customize-charts>` tab.
+Radius is measured in pixels, and defaults to ``30``. For example:
+if ten data points exist within the specified radius, the color
+displayed is based on the aggregated value of those ten data points.
+
+.. note::
+
+   Intensity shading is local to the map's current view. The most
+   intense color is displayed for the most extreme aggregated values
+   currently visible on the map, even if there are points outside the
+   current view that are more extreme.
+
+Example
+-------
+
+The following chart is based on AirBnB data for the Seattle area. It
+shows rental rate hot spots in a geospatial heatmap.
+
+.. figure:: /images/charts/seattle-airbnb-geospatial-heatmap.png
+   :figwidth: 760px
+   :alt: Geospatial heatmap example
+
+The :guilabel:`Coordinates` channel uses the ``location`` database
+field, which contains arrays of latitude-longitude pairs. The
+:guilabel:`Intensity` field uses the ``monthly_price`` database field,
+which contains monthly rental rates for each property in the database.

source/chart-type-reference/geo-spatial.txt

@@ -38,10 +38,7 @@ Heatmaps provide the following :ref:`encoding channels
        along the Y axis for each unique value in this field.
 
    * - Intensity
-     - An :guilabel:`aggregation` encoding channel that changes the
-       shading of the matrix elements to reflect the aggregated value
-       of this field. Darker colors in the visualization reflect
-       greater aggregated values.
+     - .. include:: /includes/intensity-definition.rst
 
 .. note::
 

source/chart-type-reference/geospatial-heatmap.txt

@@ -83,3 +83,4 @@ Text Charts
       /chart-type-reference/grid-charts
       /chart-type-reference/donut-chart
       /chart-type-reference/text-charts
+      /chart-type-reference/geo-spatial

source/chart-type-reference/heatmap.txt

@@ -0,0 +1,4 @@
+An :guilabel:`aggregation` encoding channel that changes the
+shading of the colors in different chart regions to reflect the
+aggregated values of this field. More intense colors in the
+visualization reflect greater aggregated values.