About adding data layers

Web maps are built by selecting a basemap, then adding data layers from services and files. New web maps include a default basemap that provides background or contextual information for additional content you place on top. You can choose a different basemap and add content from several other sources to augment what the map conveys. This additional content can come from your organization, ArcGIS Online, Esri, GIS servers that are available on your local machine or network, or servers publicly available on the Internet. You can also import local data from a file on your computer and add a map notes layer which lets you add features directly to the map. Once you've added data to your map, you can fine-tune the information by changing symbols, configuring pop-up windows, changing the extent, and so on.

What types of data layers can you add to a web map?

Data layers are directly consumable in web maps and can be referenced data layers or data layers stored inside the map.

Referenced data layers

Referenced layers are shared on the web and can be hosted on a GIS server and registered to Esri's cloud, hosted directly in Esri's cloud, or externally available on a public server. You can add the following types of layers to a web map:

• Map service
• Feature service
• Image service
• KML
• OGC WMS
• CSV

Data layers stored in the map

Static data files need to be web-enabled before they can be consumed in web map. If you have local data that includes location information, you can import it into the map where it becomes part of the map (and therefore web-enabled). You can also add a map notes layer and add feature data that is stored in the map. The following types of data can be added and stored in a web map as layers:

• Delimited text file (.csv and .txt)
• Shapefile (.zip)
• GPS file (.gpx)
• Map notes layer created in the ArcGIS.com map viewer

Adding data layers to the map

There are four ways you can add a data layer to a map:

1. Search for layers
2. Add layers from the web
3. Add layers from files
4. Add map notes

Considerations for adding data layers to a web map

• For the best performance creating web maps, it is recommended that you use Mozilla Firefox, Google Chrome, or Internet Explorer 9 or higher. Internet Explorer 7 and 8 are supported but have performance limitations when working with web maps. For example, you cannot drag and drop files onto the map, fewer features can be displayed, and you may lose your work if you leave the map viewer window without saving. If you need to use IE 7 or 8, installing Google Chrome Frame may improve your experience. The free Chrome plug-in allows your older browser to take advantage of newer web technologies in applications such as the map viewer.
• When you create a new map, you can use the default basemap that appears or choose a different basemap.
• Large amounts of data in a layer or the map may affect the performance of the map. For example, you may lose the map you are working on if you navigate away from the map viewer when the web map is too big for your browser to cache (generally, bigger than 2.5 MB, except with IE7 [64 KB] and IE8 [530 KB]). To help prevent this, sign in before you start working and periodically save your map, especially if you add a large amount of data.
• You may find that some features are missing on your map after you add a feature layer. If you imported data from a file, there are limitations on how many features the map viewer displays. For text files (.txt or .csv) with latitude and longitude information, the first 1,000 rows of features are displayed. If you use Internet Explorer 7 or 8, the first 750 rows of features are displayed. If your text files have address information, the first 250 addresses are displayed (for all browsers). For a GPS Exchange Format (.gpx) file, the first 1,000 layers of features are displayed. If you added a KML document, features from placemarks, network links, ground overlays without refresh properties, folders, and extended data are displayed. Other features are not supported at this time.
• If you add an Open Geospatial Consortium, Inc. (OGC), Web Map Service (WMS) layer to your map, you may get an error that the layer's coordinate system doesn't align with that of the basemap. This error message usually appears if you have added layers to your map, then add an OGC WMS layer that isn't in Web Mercator, the projection of the basemaps in the ArcGIS.com map viewer gallery. Create a new map and add your OGC WMS layer first. If your layer is in GCS WGS84, the ArcGIS.com map viewer uses the GCS WGS84 World Imagery basemap. If your OGC layer is in a coordinate system other than Web Mercator or GCS WGS84, your layer is used as the basemap. Now you can add additional layers.
• Tiled map services that use aerial imagery may not display on the map if you are using a Web Mercator basemap (which is the projection of the basemaps in the gallery) and the service is not in Web Mercator. To display the layer, use it as the basemap or display it on top of a basemap that is in the same projection as the tiled map service.