Using one CRS for an entire US state?

Question

I am working on a GIS project for Virginia and the data spans the entire state. There are two CRS available VA North (FIPS 4501) and VA South (FIPS 4502).

Is it possible to use just one of those CRS for the entire state, or do I have to split the data up into North and South?

Answer 1

Look for EPSG:3968, NAD83 / Virginia Lambert. There are variants using different geographic coordinate reference systems (CRS) like 3969 on NAD83 HARN, 3970 on NAD83 NSRS2007, and 6591 on NAD83 (2011). The definition came from the Virginia Information Technologies Agency.

Because it uses the Lambert conformal conic projection, that means that shapes/angles are maintained, like a State Plane zone. Here are the projection parameters:

Central_Meridian: -79.5
Standard Parallel 1: 37.0
Standard Parallel 2: 39.5
Latitude Of Origin: 36.0
False Easting: 0.0
False Northing: 0.0

Answer 2

... or do I have to split the data up into North and South?

For this part of the question, the state plane coordinate system divides a (larger) state into multiple zones in order to limit the map distortion in each zone to a certain level.

Whether you have to split the data into zones or use a CRS that covers the entire state depends on your tolerance for map distortion.

Answer 3

You can define one coordinates system for the project, and the CRS of layers located in this project will be converted to the project coordinates system but make sure 'on-the-fly re-projection' feature is active.

Steps to set project CRS:

1. Settings->Project Properties (or click on the globe symbol in the lower right corner).
2. Select the Coordinate Reference System (CRS) tab.
3. Check the Enable 'on the fly' CRS transformation checkbox.
4. Pick a suitable project CRS to work with (e.g. WGS-84).

Reference:
http://wiki.openstreetmap.org/wiki/QGIS