Why Storage Format Matters for Topographic Maps
Topographic maps issued by Natural Resources Canada (NRCan) through the National Topographic System (NTS) are printed on paper stock that responds to environmental changes over time. Folding, rolling, and improper housing each introduce different types of mechanical damage. The most common problems seen in privately held map collections are fold-line tears, edge brittleness, and ink transfer between stacked sheets.
In Canadian homes, conditions vary significantly by region and season. A basement in Winnipeg in February can drop to 15–20% relative humidity, while a Vancouver garage in July may reach 70–80% RH. Both extremes accelerate deterioration — dryness causes brittleness, excess moisture promotes mould growth and cockling.
Flat Storage: The Preferred Method
Storing maps flat — unfolded and horizontal — is the approach used by professional archives and libraries, including Library and Archives Canada. For home use, flat storage requires horizontal space but prevents the fold-line damage that accumulates with repeated handling.
Flat File Cabinets
Flat file cabinets (also called plan chests or map chests) are the most practical solution for larger collections. Standard sizes accommodate NTS 1:50,000 and 1:250,000 sheets without folding. Key considerations when selecting a flat file for home use:
- Steel cabinets are preferable to wood, which can off-gas acids over time.
- Drawer depth should be shallow enough that maps do not curl under the weight of many sheets. A maximum of 25–30 sheets per drawer is a reasonable limit for unframed maps.
- Line each drawer with acid-free barrier paper or board to separate maps from the metal surface.
Under-Bed Storage
For smaller collections — fewer than 20 sheets — shallow under-bed storage bins can work if the maps are first interleaved with acid-free tissue and placed inside a polyethylene bag to buffer against humidity fluctuations. This approach requires monitoring, as under-bed environments can accumulate dust and experience temperature swings from nearby exterior walls.
Rolled Storage: When and How to Use It
Rolling is sometimes unavoidable for large-format maps or when flat file space is not available. The key is using an appropriately sized tube and rolling with the printed side outward to reduce stress on ink layers.
Tube Specifications
- Tube diameter should be at least 10 cm. Smaller tubes create tighter curves that stress paper fibres.
- Use acid-free cardboard tubes or, preferably, polypropylene tubes. Avoid kraft paper tubes, which are acidic.
- Wrap the map in acid-free tissue before rolling to prevent abrasion and ink transfer.
- Store tubes horizontally on padded supports. Vertical storage concentrates stress at the bottom edge.
Rolled maps require unrolling for use, which introduces handling risk each time. For maps accessed regularly, flat storage is worth the additional space investment.
Folded Storage: Risks and Mitigation
Many NTS maps come pre-folded for retail distribution. Continuing to store maps in their original folded format is the most space-efficient option but introduces cumulative damage at fold lines, particularly at intersections where two folds cross.
If folded storage is the only practical option:
- Store maps in individual polyethylene or polypropylene sleeves rather than loose in boxes. This prevents sheets from sticking together and reduces abrasion.
- Do not store heavy items on top of folded map boxes. Pressure accelerates fold-line tears.
- Refold periodically along slightly different lines if the original fold lines are showing stress. This distributes the mechanical load.
Environmental Conditions for Home Storage
Temperature and humidity are the two variables with the greatest impact on paper longevity. The ranges used by professional archives — typically 15–18°C and 30–50% RH — are difficult to maintain exactly in a home setting, but approximating them consistently is more important than achieving precision.
Managing Canadian Winter Conditions
Forced-air heating in Canadian homes drives indoor humidity below 30% RH during winter months, particularly in prairie provinces. At these levels, paper loses flexibility and becomes prone to tearing during handling. Options for buffering this:
- A room humidifier near the storage area, set to maintain 40–45% RH.
- Storing maps inside sealed polyethylene boxes with silica gel packets calibrated to 45% RH. These packets are available from archival suppliers and need periodic regeneration.
Managing Summer Humidity
In humid regions — coastal British Columbia, southern Ontario, Quebec — summer months can push indoor humidity above 60% without air conditioning. At this level, paper absorbs moisture, causing cockling and creating conditions for mould. Dehumidifiers or air conditioning in the storage room address this directly. Basements require particular attention, as they are prone to ground moisture intrusion.
Enclosure Materials
The materials that contact maps directly — folders, sleeves, interleaving tissue — should meet archival standards for paper preservation. The relevant standard for Canada is ISO 9706, which specifies requirements for paper permanence, or suppliers can provide products that meet Library of Congress or Canadian Conservation Institute guidelines.
Acceptable materials include:
- Acid-free, lignin-free paper folders (pH 7.0–8.5)
- Polyethylene or polypropylene sleeves (avoid PVC, which degrades and off-gasses plasticizers)
- Acid-free tissue for interleaving and wrapping
- Inert foam padding for drawer liners
Useful References
- Canadian Conservation Institute (CCI) — publishes care and handling guides for paper documents
- Natural Resources Canada — Topographic Information — source for NTS map specifications
- Library and Archives Canada — provides guidance on personal archiving
Last updated: May 22, 2026