Editing Map (section)

===Electronic===<!-- Electronic map redirects here -->
{{Further|Web page|PDF#Optional Content Groups (layers)|MapQuest|Google Maps|Google Earth|OpenStreetMap|Yahoo! Maps}}
[[File:Topographic map example.png|thumb|A [[United States Geological Survey|USGS]] [[digital raster graphic]].]]
From the last quarter of the 20th century, the indispensable tool of the [[cartographer]] has been the computer. Much of cartography, especially at the data-gathering [[surveying|survey]] level, has been subsumed by [[geographic information system|geographic information systems]] (GIS). The functionality of maps has been greatly advanced by technology simplifying the superimposition of spatially located variables onto existing geographic maps. Having local information such as rainfall level, distribution of wildlife, or demographic data integrated within the map allows more efficient analysis and better decision making. In the pre-electronic age such [[superimposition]] of data led [[John Snow (physician)|Dr. John Snow]] to identify the location of an outbreak of [[cholera]]. Today, it is used by agencies around the world, as diverse as wildlife conservationists and militaries.

[[File:Maps-for-free Sierra Nevada.png|thumb|[[Topographic map|Relief map]] of the [[Sierra Nevada]]]]

Even when GIS is not involved, most cartographers now use a variety of computer graphics programs to generate new maps.

Interactive, computerized maps are commercially available, allowing users to ''zoom in'' or ''zoom out'' (respectively meaning to increase or decrease the scale), sometimes by replacing one map with another of different scale, centered where possible on the same point. In-car [[global navigation satellite system]]s are computerized maps with route planning and advice facilities that monitor the user's position with the help of satellites. From the computer scientist's point of view, zooming in entails one or more of:

# replacing the map by a more detailed one
# enlarging the same map without enlarging the [[pixel]]s, hence showing more detail by removing less information compared to the less detailed version
# enlarging the same map with the pixels enlarged (replaced by rectangles of pixels); no additional detail is shown, but, depending on the user's vision, possibly more detail can be seen. If a computer display does not show adjacent pixels really separately, but overlapping instead (this does not apply for an [[Liquid crystal display|LCD]], but may apply for a [[cathode-ray tube]]), then replacing a pixel by a rectangle of pixels does show more detail. A variation of this method is [[interpolation]].

[[File:World.pdf|thumb|A world map in PDF format.]]

For example:
* Typically (2) applies to a [[Portable Document Format]] (PDF) file or other format based on [[vector graphics]]. The increase in detail is limited to the information contained in the file: enlargement of a curve may eventually result in a series of standard geometric figures such as straight lines, arcs of circles, or [[spline (mathematics)|splines]].
* (2) may apply to text and (3) to the outline of a map feature such as a forest or building.
* (1) may apply to the text as needed (displaying labels for more features), while (2) applies to the rest of the image.  Text is not necessarily enlarged when zooming in. Similarly, a road represented by a double line may or may not become wider when one zooms in.
* The map may also have layers that are partly [[raster graphics]] and partly [[vector graphics]].  For a single raster graphics image (2) applies until the pixels in the image file correspond to the pixels of the display, thereafter (3) applies.