San Vicente map MapGazer – using map tools


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Using map tools

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Every map has one or more zoom levels, or layers, which can present a view of the map at a different scale. Zoom level 0 is the least detailed (it can show most of the globe as one small image) whereas (for example) 1:25,000 topographical maps are typically presented at zoom level 15 or 16.  The scale at a given zoom level differs from the one above or below it by a factor of two.

MapGazer provides several Map tools to help you manipulate map layers (for example, to copy maps from different sources to make new composite maps).  You can access these map tools either from the main menu (Map→Map tools) or by right-clicking on the map and selecting Map tools from the pop-up menu.  You can also create a subsection of a map from the current view or an Area.

Selecting a map tool starts an operation that works in the background. A Progress dialog showing the progress of the operation (with the opportunity to cancel) will be shown.

Since these operations might involve Gigabytes of data they cannot be undone – and if cancelled, they might leave partial (but consistent and usable) results.  Before using these tools take backups, as appropriate.

Maps are generally written using JPEG tiles, but if a source map uses PNG tiles then the target will be written with those PNG tiles to preserve transparency (e.g., in Spanish Geological maps).

The following tools are available; to avoid conflicts only one can be used at a time:

  • Copy current map layer to – copies the current layer to a different map.

    If you choose this, you will be prompted to select the target map (use New Folder to create a new map), and once selected the current map layer will be copied to the target map.  All the map tiles from the source (current) map are copied to the target map and will replace any that already exist in the target map.  Note that if the target map is empty it will usually be faster to copy the map using the operating-system copy (e.g., drag and drop).

  • Compress current map layer to – the current layer is compressed to a map layer at the next level out (that is, at zoom level less one) to a selected map (which may be the current map).  The map tiles from the source layer are compressed by a factor of two in each dimension to maintain the correct scale.  Creating a layer by compressing a more detailed one can be useful when only a few source layers are available or if a layer has been poorly compressed at source.

    If you choose this, you will be prompted to select the target map (use New Folder to create a new map), and once selected a compressed version of the current map layer will be copied to the target map. The compressed map tiles from the source (current) map will replace any corresponding tiles in the target map, even if the target map is the source map.

    Compression can take some time for large map layers because new tiles are being created (one for each four tiles in the source map).  When choosing which layers to compress and which to simply copy, it can be helpful to first experiment with a small subset map (see Save view as map, below) – for example, by making compressed versions of all layers in a map as a new map then comparing the maps at the various zoom levels by either opening two view windows or overlaying one map on the other.

  • Save view as map – create a subsection of the map using current view

    This creates a subset map that includes the tiles currently in view, for all layers available.  If you choose this, you will be prompted to select the target map (use New Folder to create a new map).

    The target folder (map) may already have data. In this case the target map must be compatible (that is, have the same number of tiles per file). If both source and target contain the same tile then the source tile is used (written), using the source tile’s format (JPEG or PNG).

    Writing a subset map onto an existing map could cause problems because the maps might use different directory names. To try and alleviate the latter difficulty the stub for directories is taken from any existing subdirectories, or if none then the name of the target parent folder (the map name) is used.

    A subset map can then be used as a source or target for any of the operations described above, just like any other map.

    You can also create a subset map by defining an Area; for more details, see: Using areas, ‘save a subsection of the map’.

  • Delete current map area – delete the current layer.

    This will delete the tiles in the current layer.  This is a permanent deletion, so, as for the other map tools, MapGazer will ask for confirmation before proceeding.  Currently, you cannot delete the only layer in a map using this tool.

MapGazer and these web pages were written by Mike Cowlishaw; Please send me any corrections, suggestions, etc.
All content Copyright © Mike Cowlishaw, 2014–2022, except where marked otherwise.  All rights reserved. The pages here, and the MapGazer program, are for non-commercial use only. Privacy policy: the Speleotrove website records no personal information and sets no ‘cookies’. However, statistics, etc. might be recorded by the web hosting service.

This page was last updated on 2021-05-01 by mfc.