MassGIS data can be divided into two broad categories: base map data and environmental data. As described below, these data have been developed at a variety of scales (see the section Understanding Scale below for a brief description on map scale). The data may also be categorized further, based on types of geographic features, such as infrastructure, physical resources, and political boundaries. This page describes the two broad categories. For descriptions on individual layers see the Available Datalayers page, on which the data are organized within the more-detailed categories. To receive data, please visit the Free Download area, or the Order Maps & CDs section.

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Note on using MassGIS data:
When using MassGIS data on maps or in digital applications, source credit should be stated as "Office of Geographic and Environmental Information (MassGIS), Commonwealth of Massachusetts Executive Office of Energy and Environmental Affairs"
 

Base Map Data

In its role as a repository for GIS data, MassGIS is responsible for maintaining the "base map" datalayers which commonly appear on many kinds of maps. These datalayers include features such as roads, streams, and political boundaries--relatively permanent, widely used features. Many of the base map datalayers maintained by MassGIS have been derived from U.S. Geological Survey data and represent many of the feature types found on USGS topographic maps. More recently developed data were derived from the digital orthophotos providing improved basemap accuracy.

Several of the MassGIS base map features are available in two scales. So-called "Quad" scale datalayers were typically compiled from 1:25,000 scale maps (the scale used on the popular USGS 7.5 minute topographic map quadrangles) and are suitable for spatial analysis of larger areas such as counties or of entire towns. MassGIS is making increasing amounts of large scale data available which is suitable for spatial analysis within towns or of individual parcels of land. Large scale data have been developed from the EOEEA digital orthophotos. This 1:5,000 scale base map is now considered the new state basemap for data. Other datasets have been developed at smaller scales (1:100,000 or 1:250,000). The individual description pages state the layer's scale.

In addition to vector (point/line/area) data, MassGIS also distributes raster (image) data (ortho images, scanned USGS quads, impervious surface, and others). The imagery is available in Tiff and MrSID , JPEG 2000 and ERDAS Imagine formats.

Environmental Data

In addition to base map data, MassGIS distributes datalayers developed by EOEEA and its agencies. These datalayers include those developed by the agencies for the purpose of enforcing environmental regulations or in support of various types of environmental analysis. Responsibility for maintaining and updating these datalayers remains with the agencies which produced them, as indicated in the individual descriptions. Many of these datalayers were compiled at "Quad" scale and are suitable for spatial analysis using the MassGIS base map data.

Scale is defined as the ratio of the distance measured on a map to that measured on the ground between the same two points, in the same units). Scale is represented on this web site as a ratio, such as 1:25,000 (read "one-to-25,000") which means one inch measured on the map equals 25,000 inches in the real world). Scales are relative: the term "large scale" describes data with more detail than "small scale" data. For example, data at 1:25,000 is at a smaller scale than data at 1:5,000, but at a larger scale than data at 1:100,000. In other words, the larger the ratio, the smaller the map scale. Therefore, a map of the world would have a very small scale, whereas a map of a town center will have a large scale.

GIS data can be displayed at any scale, but disregarding the scale of the source material can create problems. For example, if contour lines compiled at the very small scale of 1:250,000 are displayed at 1:25,000 with water resource features developed at much larger scale of 1:25,000, contour lines will appear to cross lakes and ponds --an obvious error.  GIS data should not be displayed beyond the accuracy at which the data was developed.

Last Updated 11/19/2009
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