What is the difference between ANSi and ISo drafting Standard?

some basic, visual differences between the two standards in terms of drafting:

ANSI dimensions are read horizontally. ISO dimensions are parallel to the dimension line.

ANSI dimensions are centered on the dimension line. ISO dimension are placed above the dimension line.

ANSI tends to use abbreviations. ISO uses symbols. (example: RAD, DIAM, 3 PLACES versus R, Ø, 3X)

dimensions have a different syntax.
ANSI: 1.000 DIAM 3 PLACES
ISO: 3X Ø 1.000

see attached picture

Addendum: Generally speaking, ISO drawings typically use First Angle Projections for view placement with dimensions in millimeter units. ANSI drawings typically use Third Angle Projections with dimensions in inch units

Many companies have their own drafting standard which is often a combination of ISO and ANSI.

Edited to answer comment down below also:
http://www.eng-tips.com/viewthread.cfm?qid=228088

This was written by someone else (link at end) but does a very well job of defining the differences between the two:

The American National Standards Institute (ANSI, /ˈænsi/ an-see) is a private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States.

The organization also coordinates U.S. standards with international standards so that American products can be used worldwide.

ANSI accredits standards that are developed by representatives of other standards organizations, government agencies, consumer groups, companies, and others. These standards ensure that the characteristics and performance of products are consistent, that people use the same definitions and terms, and that products are tested the same way. ANSI also accredits organizations that carry out product or personnel certification in accordance with requirements defined in international standards.

[4]

The organization's headquarters are in Washington, DC. ANSI's operations office is located in New York City. The ANSI annual operating budget is funded by the sale of publications, membership dues and fees, accreditation services, fee-based programs, and international standards programs…

he Institute administers nine standards panels:
•ANSI Homeland Defense and Security Standardization Collaborative (HDSSC)
•ANSI Nanotechnology Standards Panel (ANSI-NSP)
•ID Theft Prevention and ID Management Standards Panel (IDSP)
•ANSI Energy Efficiency Standardization Coordination Collaborative (EESCC)
•Nuclear Energy Standards Coordination Collaborative (NESCC)
•Electric Vehicles Standards Panel (EVSP)
•ANSI-NAM Network on Chemical Regulation
•ANSI Biofuels Standards Coordination Panel
•Healthcare Information Technology Standards Panel (HITSP)

where as ISO!!

The International Organization for Standardization (ISO) is an international standard-setting body composed of representatives from various national standards organizations.

Founded on 23 February 1947, the organization promotes worldwide proprietary, industrial and commercial standards. It is headquartered in Geneva, Switzerland,

[5]

and as of 2015 works in 163 countries.

[6]

It was one of the first organizations granted general consultative status with the United Nations Economic and Social Council.

ISO, the International Organization for Standardization, is an independent, non-governmental organization, the members of which are the standards organizations of the 163

member countries. It is the world's largest developer of voluntary international standards and facilitates world trade by providing common standards between nations. Nearly twenty thousand standards have been set covering everything from manufactured products and technology to food safety, agriculture and healthcare.

Use of the standards aids in the creation of products and services that are safe, reliable and of good quality. The standards help businesses increase productivity while minimizing errors and waste. By enabling products from different markets to be directly compared, they facilitate companies in entering new markets and assist in the development of global trade on a fair basis. The standards also serve to safeguard consumers and the end-users of products and services, ensuring that certified products conform to the minimum standards set internationally.

IT depends upon where you are working and whom you are working!!

If you are working for American based product then ANSI will come first and rest ISO will come

Credit due to:
https://www.quora.com/What-is-the-difference-between-ANSI-and-ISO

I asked about their drafting standards difference?