How do shape files define a physical location?

[RusselQuan]

How do shape files define a physical location?   When looking at the attributes of a polygon record, I see a Shape_Length and Shape_Area.  The shape can be so complex but the definition seems extremely simple.  Very curious....

[SepheFox]

Russel, I found an article that might help you immensely: A Framework for GIS Modeling

[RusselQuan]

Sephe,

Very interesting article.  I particularly liked seeing the database structure from points to arcs to features.  I see that @Joseph K Berry has quite a bit of information on line and in text.

RQ

[NeilAyres]

The *prj file (or the coordinate system definition) is part of the metadata of the feature. The coordinates in the "blob" are just a bunch of numbers. Without knowing what those numbers represent, ie the projection that they are in, the system would still not know how to map these coordinates on to a map in their correct real world location.

[RusselQuan]

You guys are great.  Thanks for all the input and links.  They are greatly appreciated and helpful.

With your help and exercises in Chapter 4 of GIS Tutorial 1 by Wilpen Gorr, I've been able to deduce the following.

zip files can originate from many sources.  I have found the US Census county zip files here.

Index of /geo/tiger/TIGERrd13/COUSUB10

The zip file has the following

.xml - the Description of the data, the extents, the link, all of the meta data about the data.

.dbf - I'm assuming this is storing all of the BLOBs.  I don't know which editor to use to read it.

.shp - the Shape file that gets imported into the GeoDatabase.gdb file and becomes a Feature Class. It must have a relationship to the .dbf file.

.prj - the DATUM, coordinate system, that is used as the foundation for the geometries.

.shx - mystery to me.

The shape file can be added to the GeoDatabase in ArcCatalog.

The GeoDatabase can then be used in ArcMap.

The Feature class can then be added to the Table of Contents on a Layer.

Please add any comments or corrections.

Next question then becomes, is it a best practice to use that geodatabase as the default geodatabase in the mxd properties?

This is going to lead to another topic and another thread of pacakaging mxds and gdbs for distribution.