Example: Overlay Containing

To explore the use of Overlay templates in the Transform pane we consider a quick tutorial example, using Overlay Containing.   One of the most common uses of overlays is to transfer fields from areas to points that are contained in those areas.    Tasks such as transferring a census block group number or zip code number from a drawing of areas to points that fall within each area are extremely common.    


 User interfaces for the Transform pane have been changed.  See the Transform Reference topic for guides to new interfaces while this topic is updated.  Use the Join dialog for spatial overlays instead of the Transform pane.


Overlay templates alter fields in the drawings upon which they work, in contrast to Topology Overlays templates which alter objects in the drawings upon which they work.


Overlays in ESRI nomenclature are called spatial joins in the data science / IT world, two different terms to describe exactly the same thing.  Manifold provides overlay templates in the Transform pane so ESRI users have a familiar way to do overlays, but the point-and-click Edit - Join dialog is a more modern way to do the same jobs with easier workflow.   Overlays, for example, always create a new component while Edit - Join updates the target table or drawing in place.   Even skilled ESRI people often prefer Edit - Join.   See the Edit - Join topic for a step by step example that duplicates the example below.


In this example we will transfer the name of a French region, called a Province in this example, to the points that represent cities which fall within each province.   If we've always wondered whether the city of Nevers was located in Bourgogne or in Centre, assigning a province to each city will let us know.



We begin with a map that has two drawing layers, a drawing called Provinces that shows the regions of France as area objects, and a drawing called Cities that shows some of the larger cities in France as point objects.  In the above illustration we have double-clicked the Cities tab to hide that layer.



When we open the Provinces Table we see it has two fields, a Province field of type nvarchar that gives the name of the region, and a Geom field of type geom that stores the geometry of the area.



If we double-click the Provinces layer tab to hide that drawing and then double-click the Cities layer tab to show that layer, we see the points in the Cities drawing.



Opening the Cities Table we see it also has two fields, a City field of type nvarchar that gives the name of the city, and a Geom field of type geom that stores the geometry of the point.   The data set came from the US military, so some of the city names such as Alencon also have the name of the airport appended, Valframbert airport in the case of Alencon.


Our task is to modify the Cities Table so it gains an additional field, Provinces, which will provide the name of the region which contains each city.



We double-click the Provinces layer to turn it back on (not required, but it helps to see what we are doing), and then we click on the Cities layer tab to make the Cities drawing the active drawing.


We launch the Transform pane.  The pane automatically configures itself to work with the active layer as the target drawing and the Geom field as the target field.



We enter the letters over into the filter box, to reduce the very long list of templates to those which contain that text, such as the Overlay Containing template we will use.  We choose the Overlay Containing template, choose the Geom field as the target, and we leave the default choice of the Provinces drawing as the Overlay.  



In the map window Manifold helpfully renders the Cities points in blue preview color to show us the Cities layer is the target of the transform.  



Back in the Transform pane we click on the Options button.



The Transform Options dialog allows us to specify the name for the resulting modified components and also allows us to specify which fields we want to transfer.



We do not need the mfd_id or Geom fields from the overlay drawing so we will Ctrl-click on each of those fields in turn to select them.   We then double-click into either of the transfer method cells for the selected records and then in the menu of methods that pops open we choose ignore.     Depending on the data type of the selected field we double-clicked, the menu of transfer options can be very long or relatively short.



Changing a transfer method for any selected row changes it for all selected rows.   To keep the display from being cluttered an ignore choice is shown as a blank in the transfer column for fields that are to be ignored.   


We want to copy the name of the Province so that we leave as is.   We press OK to apply the changes made to the transform options.



Back in the Transform pane we press the Add Component button to create new components in the Project pane, which will incorporate the modifications we want to make to the target drawing.


Two new components are created in the project: a Cities Table Overlay Containing table and a drawing to show the contents of that table called Cities Table Overlay Containing Drawing.



Opening the table we see it contains a new field with the region for each city.  The new field is called O_Province to indicate it came from a field originally called Province and is the result of an Overlay.



Dragging an dropping the new overlay drawing into our map, and turning off the Cities layer for clarity, we see the new overlay drawing of city points is the same (except that as a new drawing it uses default formatting) since the overlay only transfers fields and makes no changes to the geometry of the objects.


So in which region is Nevers located?    We click on the Cities Table Overlay Containing table and then choose Edit - Find to launch the Find dialog.


Enter Nevers, and press Next.

We can see from the table that Nevers is in Bourgogne.    We can Ctrl-click on that record to select it, showing it in the table in red selection color.



The corresponding point in the drawing will also be displayed in red selection color, showing us where Nevers is located.


Tech Tip:  The Home key is particularly useful in tables because it will always move the cursor to the first field and also will scroll the table so that the current cell is in view.   For example, if we use Edit - Find to find a record to scroll to that record we press the Home key to quickly bring it into view.



Multiple records - Some of the illustrations of tables show more than one record for various regions.   Why is that?  GIS data will often use multiple records for each area that makes up a particular region.   For example, the region of Bretagne (known in England as Brittany) includes many islands, each of which is a separate area object in this data.


Never say Nevers - The final "s" in Nevers is silent.  The name of the city is pronounced "neh-VAIR" with the stress on the second syllable.


Old Data - The illustrations in this topic use data from the US military, which show the regions of France as they were before 1 January 2016, when a law passed in 2014 took effect that reduced the number of regions in France from 22 to 13.  Centre is the same it was with just a change of name.   Nevers is still in what was Bourgogne, which expanded in 2016 to join with Franche-Comté to become Bourgogne-Franche-Comté.


Provinces vs. Regions - The drawing is called Provinces and not Regions because it was clipped out of a larger data set showing provincial boundaries for the entire world.  Around the world sub-national divisions such as US states or French regions are called many different things, but the word provinces seems to have become a reasonably generic word that militaries and others engaged in mapping often use.   State is rarely used because in many cultures it is a synonym for country and thus does not capture the notion of the administrative sub-units of a given country.


Centre vs. Centre-Val de Loire  - The region referred to as Centre in this topic was called Centre until 2015, when the new name of Centre-Val de Loire took effect, perhaps in an effort to boost tourism to the genuinely wonderful valley of the Loire river, home to what is perhaps the largest concentration of classic chateaux anywhere in the world.  To this day, everyone still calls the region Centre.  


Bourgogne / Burgundy -  Bourgogne is the French name for the region Brits and other English speakers call Burgundy.   It is justifiably famous for its wines, as also are the other big wine-exporting appellations such as Bordeaux.   Bordeaux is fine, but local people in France will often choose Chinon, from the valley of the Loire, or some other fine wine that is not so widely exported or well-known outside of France.


See Also

Select Pane


Style Pane


Transform Pane


Topology Overlays


Example: Overlay Contained -  A frequent use of overlays is to sum the values of many points that fall within an area and to transfer that sum to a new field for an area.  In this example we take a drawing that has cities in the US with a population value for each city.  We use Overlay Contained  to sum the population of each city within a state and to transfer that sum to a total population for the state.


Example: Overlay Topology Intersect - In this example we use the Overlay: intersect template in the Transform pane to trim a drawing of points so that all points which do not fall within areas in a second drawing are deleted.   The drawing of points we trim will become the US cities drawing that is used in the Example: Overlay Contained topic.


Example: Transfer Options and Merge Areas - Using the Merge Areas Transform pane  template, an exploration of the difference between using Copy and Sum for transfer options.