What is GIS?

What is a Geographic Information System?
GIS stands for geographic information system. A GIS is made up of digital map layers, each with an underlying database. Each map layer has real world coordinates so that layers can be overlaid to view map layers in relation to other map layers. Each layer's database contains information about the map features in that layer. For example, the streets layer contains information about whether a street is paved or unpaved.  This information is stored in the database for each street.  Database information can be queried or used to color-code the map. In addition, external databases can be joined to a map layer so that additional information can be displayed on a map. GIS is intelligent mapping. 
How is GIS used in Reading?
GIS provides Town staff a powerful tool to make better decisions through query and visualization of geographic information. In Reading, the Technology Division is responsible for implementing GIS technology throughout all Town departments. The GIS Administrator is tasked with: 
- developing and maintaining map layers, 
- preparing maps for Town staff, boards and committees, 
- developing web mapping applications,
- performing complex spatial analysis, 
- integrating database information between departments, and 
- providing GIS data and software for GIS users in other town departments. 
How does GIS differ from on-line sites such as MapQuest, Google Maps, or Bing?
On-line mapping sites are primarily "viewers", while GIS is primarily an analysis tool. GIS uses spatial analysis tools to, for example, notify abutters to a proposed subdivision, calculate impervious surface areas, or find properties over a given size within a particular zoning district.  Recently completed water and sewer GIS layers will be used to plan the replacement of older pipes, and could be used to notify home owners affected by a water main break.  GIS can be a regulatory tool, an asset maintenance tool, or a public safety tool.  In Reading, we strive to maintain current map layers and build new map layers to support the types of analysis that Town staff are doing now or that they may need in the future.
Where does Reading's GIS data come from and how often is it updated?
The Town's most important GIS layers are developed by or for the Town of Reading.  These include parcels and "planimetric" layers such as building footprints, roads, sidewalks, driveways, parking areas, streams, and wetlands.  Parcels are updated annually by Town staff.  Planimetric layers are created by tracing around features visible in aerial photographs.  Ours are based on 2008 aerial photos.  A flyover was completed in spring 2015 as well; data will be developed soon. Smaller datasets such as zoning, school districts, snowplow routes, and historic properties are created and updated in-house as needed. Utility data such as water, sewer, and stormwater layers are usually created by consultants and updated in-house.  MassGIS, the state's GIS agency, is another important source of data; these layers include flood zones, vernal pools, highways, and many other state-wide layers.
Plain Language Disclaimer 
GIS maps are for planning purposes only. Please refer to the primary source of the data (deeds, engineering plans, town bylaws, etc.) in all decision making. Each GIS layer is from a different source and accuracy varies. Map layers may not overlay perfectly and may be out of date. The frequency of map and data updates varies. Please use good judgement in making inferences and refer to text on each map for the date and currency of the data.