GIS Overview

A geographical information system (GIS) contains linked data with a digital map and digital database.  It is a form of computer mapping.

GIS Product Gallery Common GIS Operations Database symbolization

Table view  A database table with additional information about the records from the map.

Map view. Map locations: points, lines, or areas. Control map display with Plot button options.  Most current GIS applications use vector data. Graph View
The GIS allows multiple views of the data.  Clicking on a point or record in one view lets you see the same data in the other views.

  In MICRODEM, you should open a base map before you open a GIS data base. This can be a local or global map.  Then  Database (shapefile) on the map toolbar or Database, Load on the main menu opens a database over the map.

The database will be associated with the current map window. A table display window will open, and remain visible as long as the database is open. You can perform operations on the database

Much of the power of the GIS comes from the ability to filter data, or restrict what is shown on the map or used in statistical computations,  based on logical criteria, or geographic regions. Another strength is visually querying the data, clicking on a record on either the map or table and seeing the data in another view. You can further query graphs derived from the data, and see the record in the table or on the map. This ability to rapidly move among three different views of the data makes one of the key contributions of GIS. This power comes with a price, and you must always be aware whether the program is showing you the entire data set or a subset that you have filtered. In MICRODEM the number of active records is always shown on the bottom of the table base display table.  The "All Recs" button will only be enabled when the data has been subset.

You can also perform statistical operations, on either the entire database or a filtered subset.

Table display window

The data base display view. Each column corresponds to a field in the data base, and each row represents a record.

Because the "All recs" button is enabled, this database has been filtered, either with the "Filter" button or the "Map query" button. Any analyses will use only this data.

Map window

Map view of the database. In this case color corresponds to the type of fault believed responsible for the earthquake. The database has been filtered to display only the data within the selected block.

Graph Views.  Two dimensional graph of the data, from two fields selected from the data base. The y-axis is reversed, a common convention in earth sciences that go down into the earth like oceanography or geology.

Because this graph is linked to the data table and the map, clicking on a point on the graph will highlight its location on the map, and its position in the data table so that you can see the other characteristics of the point.

You can also get histograms, and other specialized graphs for particular data sets (like earthquake focal mechanisms, Koppen climographs).

Default options affecting GIS and database operations.

Database auxiliary files.

Reserved field names.

GIS examples:

Last revision 3/29/2019