ArcGIS Field Maps is a mobile application that allows you to capture and edit location data directly from your phone, using your device's built-in GPS and an interactive map. When collecting data in the field, you may notice that points, lines, or polygons are not positioned as accurately as expected. Distances may seem slightly off, or your features may not align well with reference datasets such as orthophotos, sewer infrastructure layers, tree layers...
In many cases, the issue is not caused by the GPS itself, but by how your web map and application have been configured. The good news is that you can significantly improve accuracy with a few simple settings, no additional hardware required.
This article will walk you through two key areas: first, how to configure your web map for optimal spatial accuracy, and second, how to get the most out of ArcGIS Field Maps' built-in positioning settings.
Many web maps are created using the default coordinate system: WGS 1984 Web Mercator (WKID 3857). This is because this projection is widely used on the internet, following Google Maps' lead. Most standard Esri basemaps use this projection system as well. But it is not the best for precision work.
Web Mercator preserves angles and shapes, which makes it great for navigation, but it does not preserve areas. The further you are from the equator, the more surfaces appear stretched and distorted. In Belgium, located around 50°N, this can have a noticeable impact when collecting field data that needs to align precisely with your reference data.
For fieldwork requiring reliable positioning using a local projected coordinate system is strongly recommended, as it minimizes distortion within a particular country or region.
For Belgium, it is strongly advised using Belgian Lambert 2008 (WKID 3812).
For Luxembourg, the use of LUREF Luxembourg TM (WKID 2169) is advised.
The best moment to improve accuracy is before the fieldwork even starts. When preparing a web map for ArcGIS Field Maps, follow these steps:
Step 1: Prepare Your Data in the Correct Coordinate System
First, ensure that your feature layers are stored in the appropriate local projection. This avoids unnecessary on-the-fly reprojection and ensures better consistency between datasets.
Step 2: Configure the Map in ArcGIS Pro
Before publishing your web map:
open your project in ArcGIS Pro,
set the map coordinate system to the appropriate local projection
verify that all layers align correctly,
add symbology, configure forms, pop-ups, and editing settings,
and publish the web map to ArcGIS Online or ArcGIS Enterprise.
When the web map inherits the correct coordinate system from ArcGIS Pro, measurements and editing in Field Maps become much more reliable.
Step 3: Prepare the Web Map for Field Maps
Once your web map is published, open it in Field Maps Designer. With Field Maps Designer, you can prepare the maps mobile workers use to complete work in the field. You can set up tasks and build forms for data collection, enable maps for offline use, configure a variety of settings, and share the map so everyone in your team can access it in Field Maps.
Even without external GPS equipment, ArcGIS Field Maps already includes several options to improve data collection quality. These can directly be adapted in the mobile ArcGIS Field Maps application. Go to ‘Your Profile’ and select ‘Collection settings’.
You can define a minimum acceptable GPS accuracy before a point can be collected, preventing users from capturing data when the signal quality is too low. This can be combined with a confidence level setting to help standardize data quality across field teams.
GPS Averaging allows the application to collect multiple GPS readings for the same position and calculate an average location. This reduces occasional GPS fluctuations and improves overall consistency. For many workflows, enabling GPS averaging already provides noticeably better results without requiring additional hardware.
Improving accuracy in ArcGIS Field Maps is not only about using advanced GPS receivers. A large part of the data quality depends on a proper preparation.
For optimal results, combine:
a local projection adapted to your region,
a properly configured web map,
appropriate Field Maps accuracy settings
When additional precision becomes necessary, external GNSS equipment with RTK corrections can take your data collection even further.
In future articles, we will explore how to use additional hardware and/or RTK corrections to increase your positioning accuracy.