Overview
MassGIS data are collected from myraid sources. The data holdings are from Federal, State and Local government agencies, non-profits and from the private sector. 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 is categorized based on types of geographic features, such as infrastructure, physical resources, and political boundaries. 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 & Data 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 Information (MassGIS), Commonwealth of Massachusetts,
Information Technology Division"
| The datum for the MassGIS database is North American Datum 1983 (NAD83). The data are registered to the Massachusetts State Plane Coordinate System, Mainland Zone (Fipszone 2001). Units are meters. (Some imagery for Martha's Vineyard and Nantucket are also available in the Mass. Stateplane Island Zone). The EPSG (European Petroleum Survey Group) code for this coordinate system is 26986. The Massachusetts State Plane Coordinate System, Mainland Zone meters is defined as follows: Projection: Lambert Conformal Conic Please
note that if you are using data in other projections or in other units
(e.g. feet) your data will not be spatially aligned to MassGIS data
(unless your GIS software supports on-the-fly projection). |
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, schools 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 developed by other state agencies and derived from the digital orthophotos providing improved basemap accuracy.Environmental DataSeveral 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 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.
In addition to base map data, MassGIS distributes datalayers developed by EOEEA and its agencies, as well as data from Federal 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 that produced them, as indicated in the individual descriptions. Many of these datalayers were compiled at "Quad" or larger scale and are suitable for spatial analysis using the MassGIS base map data.
Understanding Scale
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.