Web Mercator
The Standard for Sharing Data
on the Web
Many organizations use geographic information system (GIS) data stored in a local
projected coordinate system. When preparing to share maps or layers on the Web, it is
recommended to reproject your source data to the Web Mercator coordinate system.
Doing so will ensure that your map data is located correctly and aligns properly with
other services such as popular content providers Microsoft
®
Bing
™
Maps, Google Maps
™
,
and ESRI
®
ArcGIS
SM
Online, which have standardized their services on the Web Mercator
coordinate system.
Projecting Your Data to Web Mercator
In ArcGIS
®
, you have two options if you want to reproject your data to the Web
Mercator coordinate system. The rst, using the Project tool, creates a copy of your
data that replaces the original coordinates in your source data with new coordinates
from the Web Mercator coordinate system. The second, setting the ArcMap
™
data
frame coordinate system, instructs ArcGIS to calculate the new coordinates only when
needed—leaving your source data unchanged. Since the rst option requires a complete
copy of your data to be made, you may want to use it for data that does not change
very often—such as basemaps. You can then use the second option for data that
changes often—when it would be too time-consuming to keep creating copies of your
data. Both options are presented for your reference.
For ArcGIS Server Web mapping applications, developers can use the geometry service
to reproject features before making area and length calculations. Reprojecting features
is not a problem since positional accuracy is preserved when projecting between Web
Mercator and other coordinate systems.
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