Now that there are connections to Spatial Data Bases in Map have you ever wonder what a spatial database was and how it work? I am sure most of us have created a table in MS Access at one time or another and may even link to them with the Map Explorer. But what is a “Spatial Database” and how is it different than a Access database? I will try to shed some light on what they are and how they work. First thing the big differences is they store the geometry of the features. Be it a point, polygon or line feature each data base has it’s own method of storing the feature type and the coordinates of that feature in a column in a table. For instance lets say we have a point feature at coordinate x=20 y=20. In the table under a column named geometry the value might be “point,20,20”.
Sounds simple right? Now the fun starts when we want to know is that 20,20 at lat, lon or a state plane coordinates system. That is where the “relationship”of a database comes into play.
Here is an view of an datastore in a MySQL database and all tables that belong to it. It contains only three features tables, Featureclass1 that is empty, Parcel that is storing parcel information, and UG_Services that is storing under ground electrical services.
Depending on what Database and the engine that runs that database depends on how the tables store the data or controls it, but in a nut shell the tables all relate to one another, so if you change one item in one table it may change something in another table. Another example if you look at the parcel feature table (in MySQL Administrator) you see this.
Notice the column named “Geometry” in Map when you view the table that column is not displayed. The reason is because that FDO provider is telling MAP what to display in relation to another table in the database. Don’t ask me what one I am no way a MySQL expert but I would take a guess and say one of those with F_attribute in the name.
So in a nutshell that’s what a spatial database is and how they work. If anyone is interested in downloading MySQL and try out the FDO post a comment and I’ll direct you to the FREE Spatial Database.