Recently, I saw one of these maps with buffer zones spread across the United States. Web Mercator map with km buffer zone around selected cities. A projection is the mathematical transformation of the Earth to a flat surface.
Coordinates, Tile Bounds and Projection Click on a tile to display the numerical boundaries Want to create custom map tiles from an image or geodata? It is easy to assign location to the map see video.
Maps are usable on the web, in mobile devices or desktop GIS. Read more or directly download the app Addressing tiles: The extents of all tiles as well as the zoom levels resolution in meters per pixel are predefined for the whole Earth.
Difference is only in the way how the equivalent tiles are indexed. There are three main systems of tile adressing: But for map publishing in the form compatible with all the popular interactive maps and especially for ground tile overlays you need to use Mercator map projection.
Interactive web maps are using " Spherical Mercator " system which uses Mercator projection on the sphere instead of WGS84 ellipsoid. It is defined as EPSG: Details about this system are part of Virtual Earth documentation as well as OpenLayers documentation. Spatial references, coordinate systems, projections, datums, ellipsoids — confusing?
Source code for utility calculating tile bounds I wrote a class GlobalMercator implementing all necessary coordinate system conversions in Python.
The class is documented and quite straightforward. You can also download the source code globalmaptiles. For each tile several information is printed including boundaries in EPSG:This article gives an excellent introduction into the use of handheld GPS units in back-country related activities.
It explains how to use a GPS unit, how the UTM-grid is . The web mercator projection, popularised by Google Maps, seems to be given a new EPSG code every couple of years. EPSG (Google in calculator text) was an unofficial code EPSG - is the.
Addressing tiles: same tile bounds with different indexes. Google Maps, Microsoft Virtual Earth, Yahoo Maps, and other commercial API providers as well as OpenStreetMap and OpenAerialMap are using the same projection and tiling profile and tiles are therefore compatible. A facility for converting latitude/longitude co-ordinates to co-ordinates in metres on a Transverse Mercator projection.
An Excel Workbook is also available on this page to carry out bulk conversions. Most maps that we see on the web use the Web Mercator projection. Web Mercator gained its popularity because it provides an efficient way for a two-dimen. Distance. This uses the ‘haversine’ formula to calculate the great-circle distance between two points – that is, the shortest distance over the earth’s surface – giving an ‘as-the-crow-flies’ distance between the points (ignoring any hills they fly over, of course!).