This article will give you a better understanding of what "zoom level" is - a term that a user will usually encounter when working with digital maps and aerial or satellite imagery.
Introduction
When interacting with maps on a digital screen, a user gets the illusion of exploring a single large image of an area. For quick panning and zooming for the maps, a clever mechanism is needed to avoid loading all the map data of the entire world at once. In fact, only a small subset of the whole information is loaded each time on the screen. Such maps are called digital dynamic maps which give a visualization of multiple layers of data.
If all the information on the world map is loaded at once, the map would be overfilled, difficult to read, and very slow which is why content is generalized for different zoom levels.
Maps usually show the world represented as a square for easy processing. This view is called Mercator map projection. This view is called Mercator map projection. It correctly shows straight lines, angles of directions, and accurate shapes of buildings and objects but not their relative size especially as you get closer to the polar areas.
A user can zoom in and out of a map to reveal or hide the additional details.
Contents
What is Zoom Level?
The world map is divided into a regular grid of little square areas which are called map tiles. These tiles are arranged in a pyramid with multiple floors called zoom level. At the top level of the pyramid, the tiles always contain general information (continents, oceans). As we go farther down the pyramid, we see more details (streets, buildings, etc.).
Photo: Cumbria Soaring Club (link), All Rights Reserved
In a more technical sense, zoom level is a scalar numeric integer for maps whose value ranges from 0-23 (or even higher in some cases). The lower values (0, 1, 2...) are the farthest from the earth and the smallest in scale while the higher values (...21, 22, 23) are the closest to the earth and the largest in scale.
It determines how much of the world is visible on a map. Depending on the zoom level, which represents the floor level of the pyramid, different amounts of geographic details will be displayed.
At zoom level 0, the entire world fits on a single tile, and zoom level 1 uses four tiles to render the world with a 2 x 2 square, as shown below:
Photo: Microsoft (link), All Rights Reserved
The diagram below helps to understand how detail increases with zoom level. In this diagram, we show a single tile, from zoom level 12 to 21 of a specified area in New York:
How Zoom Level Works
At low zoom levels, a small set of map tiles covers a large geographical area. At higher zoom levels, a larger number of tiles cover a smaller geographical area.
Calculating Zoom Level
At each zoom level, each tile is divided into four, and its size doubles, quadrupling the area.
Moreover, each subsequent zoom level quad divides the tiles of the previous one, creating a grid of 2zoom x 2zoom.
For instance, zoom level 20 is a grid 220 x 220, or 1,048,576 x 1,048,576 tiles (resulting in a total of 1,099,511,627,776 tiles).
To get the zoom level, the pixel dimensions of a map must be known, or vice versa. Calculations also have to be done in spherical Mercator coordinates.
The following table provides the list of values for zoom levels:
The detailed calculation for the distance per one pixel can be found here.
To discover the real-world size of a single tile on a given zoom level, we can use the formula circumference of earth / 2zoom level that produces the number of meters per tile side, where the circumference of the earth equals 40,075,017 meters.
Zoom Level and Tile Grids
To optimize the performance of map retrieval and display, a map is cut into tiles. The number of pixels and the number of tiles differ at each zoom level. Tiles are called by zoom level and the x and y coordinates, which correspond to the tile's position on the grid for that zoom level.
When determining which zoom level to use, remember each location is in a fixed position on its tile. As a result, the number of tiles needed to display a given expanse of territory is dependent on the specific placement of the zoom grid on the world map.
For example, for the two points below which are distanced 900 meters apart, it may only take need three tiles to display a route between them at zoom level 17. However, if the western point is on the right of its tile, and the eastern point is on the left of its tile, it may need four tiles:
Once the zoom level is determined, the x and y coordinate values can be calculated:
The top-left tile in each zoom grid is x=0, y=0 and the bottom-right tile is at x=2zoom-1, y=2zoom-1
Conclusion
The use of coordinate systems and map projections to transform the shape of Earth into flat maps has been around for centuries. A map of the entire world is too big to be directly displayed on a screen. Thus, a clever mechanism for quick map browsing is needed.
The world is divided into small squares, each with a fixed geographic area and scale. This clever trick allows the interaction with just a small part of a map without loading a huge global dataset, depending on the preferred zoom level.
Zoom level is an integer that specifies the level of detail to display on the map, with larger integers resulting in greater levels of detail. Selecting a higher zoom level will display better resolution for high-quality imagery, that can be used for more accurate project planning and work efficiency.
We hope that you have found this article on understanding zoom level in maps and imagery helpful. Feel free to contact us at support@plexscape.com for any questions you may still have.
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