This is a general discussion topic designed to help you understand how and where Think GIS stores its data.

Map File (.TGM or .TMA)

The Map file, or project file, is a collection of layers.  All of the lines and data that you work with in Think GIS are stored in their individual layer files (see below).  The map file simply stores a list of layers commonly used together for a specific purpose or application.  Layer Settings are also stored in the map file.  These parameters control the visibility, color, symbol, color coding rules, and other display attributes for each layer.  

It is common to have multiple map files that all utilize a common set of layer files.  This way a layer can be included in one map but not another.  Or a layer can be green in one map but gray in another.  And since the contents of each layer are stored in only one place, any changes made to a layer in one map will automatically show up on any other map using that same layer.  

Typically all the layer files (*.tml) and one map files (*.tgm or *.tma) are stored together in the same folder named according to the city, county, or region that they cover.  

Layer Files ( .TML )

Each layer stores its contents in a file named with the TML extension.  This file stores both the geometry and database information for a layer.  The contents of a layer are organized as follows:

• The primary content of a LAYER can be thought of as a database table where each row is a FEATURE and each column is a FIELD.  You can configure each LAYER with its own set of FIELDS and its own form layout used to view individual FEATURE records one at a time.  This organization is best demonstrated in the map Index.
• Each FEATURE record can be represented on the map with one or more ENTITIES.  An ENTITY is a polyline, symbol, area, label, or raster image drawn on the map.  The relationship between FEATURES and ENTITIES is a parent/child relationship where the FEATURE is the parent and then ENTITIES are the children.  Each parent can have several children and each child has only one parent.
• Example: A LAYER called "Roads" contains a FEATURE called "River Rd".  River Rd is represented on the map with 7 polyline entities each tracing a section of the road's centerline and 2 label entities marking where the FEATURE is labeled.
• The layer file also stores Advanced Layer Settings, Layer Format, Form Layout, Layer Password, Feature Links to other data, Map Projection, and other settings.