Six book boxes for Fairfax County
A worked example of how the planner chose six sites for 112,570 modeled youth, and what more boxes would add.
This is a model, not a finished project. No boxes were installed and no reading outcomes were measured. Figures come from the Fairfax demo snapshot (FFX-2026-06), recorded in September 2026.
The six-box plan at a glance
Budget
$3,000
6 boxes at $500 each
Average estimated distance
5.9 km
About 3.7 miles
Youth within 1 mile
15,020
13% of modeled youth
Combinations checked
8,008
Every 6-site set from 16 eligible sites
The starting point
- Where youth live. 39 modeled tract groups with 112,570 residents ages 0 to 17. Each group is placed at its center point.
- Where a box could go. 18 public sites: parks, rec centers, community centers, and Metro stations. Lake Accotink Park and Huntington Metro carry a flood flag in the snapshot, so they were left out, leaving 16.
- How distance is estimated. Straight-line distance multiplied by 1.35 to allow for streets. This is not a walking route.
Where the boxes go
- Selected site
- Within 1 estimated mile
- Candidate, not selected
- Excluded by flood flag
- Youth by neighborhood (larger means more)
| # | Site | Youth nearest this box |
|---|---|---|
| 1 | Willston Multicultural Center Community center · 6131 Willston Dr | 24,060 |
| 2 | Wiehle-Reston East Metro Metro station · 1908 Reston Metro Plaza | 16,090 |
| 3 | Franconia-Springfield Metro Metro station · 6880 Frontier Dr | 22,170 |
| 4 | Cub Run RECenter Rec center · 4630 Stonecroft Blvd | 19,840 |
| 5 | Gum Springs Community Center Community center · 8100 Fordson Rd | 17,170 |
| 6 | Vienna Metro Metro station · 9550 Saintsbury Dr | 13,240 |
How the planner chose them
Add one box at a time
The first pass placed each box where it cut total estimated distance the most: Providence RECenter, Reston Community Center Hunters Woods, Franconia-Springfield Metro, Cub Run RECenter, Gum Springs Community Center, and Nottoway Park.
Try swaps
Next it tried replacing each site with an unused one and kept every swap that helped.
Removed Added Distance cut Providence RECenter Willston Multicultural Center 2.8% Reston Community Center Hunters Woods Wiehle-Reston East Metro 1.3% Nottoway Park Vienna Metro 0.3% Together, the swaps brought total estimated distance 4.3% below the first pass. Two of the three new sites are Metro stations.
Check every combination
With 16 eligible sites, the planner could test all 8,008 ways to pick six. None beat the swapped set, so it is the best six-site plan for these inputs. That does not prove the sites are the best real-world locations.
What more boxes would add
The planner solved the same inputs for 3 to 12 boxes. The six-box plan is shown in dark green.
Average estimated distance
Kilometers to the nearest box
Youth within 1 mile
Estimated, of 112,570 modeled youth
Show all budgets as a table
| Boxes | Budget | Average distance | Youth within 1 mile | Share |
|---|---|---|---|---|
| 3 | $1,500 | 8.8 km | 5,330 | 5% |
| 4 | $2,000 | 7.5 km | 6,380 | 6% |
| 5 | $2,500 | 6.6 km | 10,900 | 10% |
| 6 | $3,000 | 5.9 km | 15,020 | 13% |
| 7 | $3,500 | 5.5 km | 15,020 | 13% |
| 8 | $4,000 | 5.3 km | 17,660 | 16% |
| 9 | $4,500 | 5.0 km | 17,660 | 16% |
| 10 | $5,000 | 4.9 km | 17,660 | 16% |
| 11 | $5,500 | 4.7 km | 17,660 | 16% |
| 12 | $6,000 | 4.6 km | 20,640 | 18% |
- Going from six to eight boxes costs $1,000 more, shortens the average by about 0.7 km, and brings 2,640 more youth within a mile (13% to 16%).
- Each box helps less than the one before. Going from three boxes to four shortens the average by 1.3 km. Going from eleven to twelve shortens it by 0.1 km.
- Coverage within a mile moves in jumps. The 7th, 9th, 10th, and 11th boxes bring no one new within a mile, then the 12th adds 2,980. Each neighborhood's youth are counted at one point, and the planner shortens average distance rather than maximizing coverage within a mile.
- Most youth are still far from a box. With six boxes, 87% of modeled youth are more than a mile away, and 1 in 10 is more than 10.4 km (6.5 miles) away.
What this example leaves out
- Walking routes. Distances are straight-line estimates. A short one can still cross a highway.
- Site checks. Owner permission, accessible paths, visibility, and upkeep are unverified at all six sites.
- Flood risk. The two flood flags come from the demo snapshot, not FEMA flood maps.
- Child poverty. Equity weighting is on in the planner link, but the Fairfax snapshot has no poverty data, so it does not change this result.
- Existing book access. Nearby libraries and book-sharing boxes are not counted.
Try it yourself
Open either plan, change the number of boxes or the cost per box, and export a report to share with site owners.