[Editor's note: No PRJ file? No problem. Use this new guide by M. Maher from ESRI Press to learn map projection basics and the ArcGIS commands (versions 9 and 10) that register map data to common coordinate spaces. Read the first chapter and table of contents at ESRI.]
Republished from Vector One.
‘Lining Up Data in ArcGIS‘ – a guide to map projections is a new book from ESRI Press. It is authored by Margaret M. Maher. Since I don’t have ArcGIS running in my office I couldn’t try out some of the details provided in the book, nevertheless, I did spend some time running through the book and offer the following comments.
One of the issues that many people encounter with GIS data revolves around projections, coordinates and lining up data with already existing spatial information. I’ve made the mistake myself numerous times, excited to get the data into the system, only to open the map window and finding what I just added from Berlin is placed in Oklahoma, Alberta or the middle of the Mediterranean Sea. How did that happen? Because I never lined up the data properly.
This book is very helpful. It explains how to identify geographic coordinate systems as compared to projected coordinate systems. If you are using ArcMap, then this book will show exactly how to determinine projections and set them. It even provides examples for going to ArcGIS Online, downloading imagery and aligning it properly.