Hello, I suspect that the difference between the Bonne and the UTM is partly because the Bonne used a Paris Meridian. The one map in OCLC with a Bonne projection states: Scale 1:2,000,000 ; Bonne proj., Paris prime meridian; (E 109°--E 120°/N 26°--N 10°). The Paris Meridian, which would have run through the Paris Observatory, would be 2°20′14.03″ longitude off maps using the Greenwich meridian. Linda Zellmer ----- Original Message ----- From: "Christopher Thiry" <[log in to unmask]> To: [log in to unmask] Sent: Monday, August 10, 2015 9:34:11 AM Subject: Indochine Maps -- Bonne vs. UTM Hello all, I received this very interesting email regarding co-ordinate/grid systems in South East Asia. My knowledge on this topic is very limited. Could someone help this person and reply directly to them? Thanks, Christopher J.J. Thiry Map Librarian Colorado School of Mines 1400 Illinois Golden, CO 80401 p. 303-273-3697 f. 303-273-3199 [log in to unmask] http://library.mines.edu/ From: Mardi [[log in to unmask]] Sent: Saturday, August 08, 2015 6:49 PM My name is Mardi Seng from Cambodia and I am working on a project that requires using GPS coordinates onto the 1933-1953 French-made maps (BONNE). A group of people has been searching the parameters that would give us a link between the two projections so we can place the WGS84 datum on a very old map. Background: Cambodia and Vietnam are demarcating their borders using the delimited 1933-1953 French-made (1:100,000) maps. To assist with the demarcation, they are using the 1960's US (1:50,000) maps. To make a very long story short, the Vietnamese working on this delimiting/demarcating project are technically and politically much more superior than their Cambodia counterpart and the Cambodian government has been working on this project secretly without oversight or scrutiny from the National Assembly or the public. I am working for a committee representing the National Assembly to try to provide oversight or scruitinize the demarcation process. But I am not trained in this field (I am an auditor/risk management by training) and I need to learn as much as possible in a very short time. I am asking for your help. 1. Do you know (or anyone who would know) the parameters that link between BONNE and UTM projections? 2. Would AMS have the parameters between the two projections? When AMS made the maps of Cambodia in 1960's, AMS used the French-made maps as the basis and "transferred" to the UTM grid? 3. My understanding is that there are at least 6 different versions of the 1933-1953 French-made maps. And there are many more copies such as 1) 1960's AMS 1:50,000 maps, 2) 1970's, 1990's 1:100,000 maps but on UTM grids. IF we have to reconcile or compare the authenticity of these maps, where do we start? I would appreciate it if I can have the opportunity to talk to you. Can I call you? Can I have your phone number? Thank you so much for your time. Mardi -- Linda Zellmer Government Information & Data Services Librarian Liaison to Natural & Physical Sciences & Agriculture 415 Malpass Library Macomb, IL 61455 [log in to unmask] Phone: 309-298-2723 Fax: 309-298-2791